The first approach uses a feature called Boot Camp that comes free on every new Mac. Using Boot Camp, the entire Mac is turned into a Windows PC, with the full capabilities and speed of a standard Windows machine. No trace of the Mac operating system is left running. The downside is that you can’t run Windows and Mac programs side by side.

The second approach uses one of two third-party programs to create a virtual Windows PC inside your Mac. This faux Windows machine runs at normal speeds and can operate simultaneously with the Mac’s own operating system. Programs native to each operating system can run side by side. The downside is that, because Windows doesn’t get complete control of the computer’s hardware, it isn’t quite as fast as in Boot Camp, and a few of its functions, like 3D graphics, don’t work as well.

This latter method is enabled by two excellent, closely matched $80 programs: Parallels, from a Swiss-based company of the same name, and Fusion, from VMWare, a U.S. company. It is Fusion that just got better, because VMWare just issued version 2.0 of the product with lots of new features, some of which let it catch up to the older Parallels and some of which push it ahead.

I’ve been testing Fusion 2.0 for a couple of weeks on two different Macs, and using it to run both Windows XP and Windows Vista. My verdict is that while you won’t go wrong with Parallels, Fusion edges it out as the better product.

The new Fusion 2.0 is a free upgrade for owners of version 1.0. It can be obtained at vmware.com/mac and at various retailers.

Like Boot Camp and Parallels, Fusion requires you to obtain and install a fresh, boxed, full version of Windows on your Mac. But once you’ve done that, your Mac becomes two computers in one. If you need to run programs that are available only on Windows, you can do so with ease.

For instance, as I write this column on a MacBook pro laptop, using a Macintosh word processor, I am using Fusion 2.0 to simultaneously run Google’s new Chrome browser, which is so far available for Windows only. I can switch between the two with a couple of keystrokes and copy text from one to the other.

Like Parallels, Fusion allows you to run Windows programs in one of three ways. You can see the entire Windows desktop, with Windows programs running within it, inside its own window on your Mac. Or, using a feature called “Unity,” each Windows program can float free, as if it were just another Mac program, with the Windows desktop invisible. If you minimize a Windows program, it disappears into an icon in the Mac’s Dock, just as Mac programs do.

Finally, you can devote the entire screen to the Windows desktop and hide the Mac operating system entirely.

Parallels can also do these things. Both programs can now also “mirror” your most common Windows and Mac file folders so that, for instance, all of the files in your Mac’s Pictures folder also appear in the My Pictures folder in Windows XP. This is a new addition to Fusion, as is the ability to take multiple “snapshots” of your Windows virtual machine, so if something goes wrong, you can roll back to a previous state when things were stable.

But Fusion has some other features Parallels lacks. For example, it allows you to automatically take those protective snapshots at timed intervals. It also permits you to completely customize keyboard commands so that the same common key combinations work in both Windows and Mac programs. It allows the faux Windows machine to take full advantage of multiple monitors, if you have them.

Fusion also uses a more modern and capable version of the proprietary 3-D graphics system in Windows, called DirectX. That means some Windows-only games and other programs that won’t work in Parallels will work in Fusion. I successfully tested two such programs, both from Microsoft: Worldwide Telescope and Photosynth.

And, in my experience, Fusion is a bit faster than Parallels. Both programs put a strain on your Mac when performing major tasks, like starting up or shutting down Windows. But Fusion seems to affect the Mac less. And, unlike Parallels, it can make Windows quicker by optionally assigning it control of the multiple “cores” in most modern processor chips.

Fusion also offers a one-year free subscription to Windows security software, while Parallels offers only a six-month subscription.

However, Fusion has its limits. Like Parallels, it cannot run the 3-D visual effects in Windows Vista. And, in my tests, it wouldn’t allow Windows running on one of my Macs to use the printer that was configured on the Mac, although that feature did work on my other test Mac.

In my view, Fusion is now the better choice for running Windows on a Mac virtually.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com.

Write to Walt Mossberg at mossberg@wsj.com

There are several reasons for this, including the security problems in the dominant Windows platform from Microsoft; spillover from Apple’s blistering success with its iPod music players; the fact that Macs can now run Windows programs; and Apple’s highly successful chain of company-owned retail stores.

But another key factor has been the Mac operating system, called OS X, which came out in 2001. It has proved to be as powerful and versatile for mainstream consumers as Windows, yet easier to use and more secure. And Apple has upgraded OS X far more rapidly than Microsoft Inc. has upgraded Windows, bringing out major new releases roughly every 18 months, while Microsoft struggled for more than five years to produce the latest Windows iteration, Vista, which came out in January.

On Friday evening, Apple will release yet another new version of OS X, called Leopard, to replace the current version, known as Tiger. I’ve been testing Leopard, and while it is an evolutionary, not a revolutionary, release, I believe it builds on Apple’s quality advantage over Windows. In my view, Leopard is better and faster than Vista, with a set of new features that make Macs even easier to use.

Leopard will come preinstalled on all new Macs. It can also be purchased for $129 as an upgrade to existing Macs that, depending on configuration, can be as many as six years old. Unlike Vista, which is sold in four noncorporate upgrade versions ranging from a $100 stripped-down “basic” edition to a $259 deluxe “ultimate” edition, there’s only one version of Leopard. It includes all the features, from those aimed at novices to those aimed at power users.

For me, the marquee features in Leopard are a new function called Time Machine that automatically backs up your entire computer in the background; two new methods, called Cover Flow and Quick Look, for rapidly viewing the contents of files without opening any programs; and new techniques that allow you to access the files in, and to remotely control, other computers on your network or connected over the Internet with a few clicks and no technical expertise.

Plus, Apple’s free software for running Windows on a Mac, called Boot Camp, which was formerly an add-on users had to download and install, is now built right into the operating system. And, in my tests, the third-party Fusion program for running Windows and Mac programs simultaneously continued to work fine in Leopard.

I did notice a few drawbacks, but they were minor. The menu bar is now translucent, which can make it hard to see the items it contains if your desktop picture has dark areas at the top. The new folder icons are dull and flat and less attractive than Vista’s or their predecessors on the Mac. While Time Machine can perform backups over a network, the backup destination can only be a hard disk connected to a Mac running Leopard. And, on the Web, I ran into one site where the fonts on part of the page were illegible, a problem Apple says is known and rare and that I expect it will fix.

While Apple claims the new system includes more than 300 new features, there is nothing on the list that could be considered startling or a major breakthrough. Some of Leopard’s features are unique, but many others — such as backing up data and quickly viewing files — have been available on both Windows and the Mac via third-party programs or hard-to-find geeky methods buried in the operating systems. Leopard has made them easy to find and use.

When I upgraded my personal iMac desktop to Leopard, it took less than an hour, and after the process was complete, all my programs, including the Mac version of Microsoft Office, the Firefox Web browser and Adobe Reader, worked rapidly and fine. I was still able to run Windows XP via Fusion. And my previous installation of Boot Camp, which turns the iMac into a speedy, full-fledged Vista machine after a reboot, worked perfectly. All my Vista programs and files continued to function properly.

With Cover Flow, users get a visual preview of a computer’s files without having to open programs.

In fact, every piece of software and hardware I tried on two Leopard-equipped Macs — a loaned laptop from Apple and my own upgraded iMac — worked fine, exhibiting none of the compatibility problems that continue to plague Vista. My old Hewlett-Packard inkjet printer, for which Vista lacks the proper software, worked instantly in Leopard, even over the network. And, unlike with Vista, it was able to print on both sides of the page. I popped my old Verizon cellphone modem card into the test Leopard laptop and it worked, too, with no software installation or tweaking.

Leopard felt about as fast as Tiger, and it started up much faster than Vista in my tests. I compared a MacBook Pro laptop with Leopard preinstalled to a Sony Vaio laptop with Vista preinstalled. Even though I had cleared out all of the useless trial software Sony had placed on the Vaio, it still started up painfully slowly compared with the Leopard laptop.

It took the Vista machine nearly two minutes to perform a cold start and be ready to run, including connecting to my wireless network. The Leopard laptop was up, running and connected to the network in 38 seconds. In a test of restarting the two laptops after they had been running an email program, a Web browser and a word processor, the Sony with Vista took three minutes and 29 seconds, while the Apple running Leopard took one minute and five seconds.

Here’s a rundown of some of Leopard’s key features. Much more detailed information is available at apple.com/macosx.

File management: Apple’s Finder, the equivalent of Explorer in Windows, now offers two new ways to quickly see what your files contain. You can still view them as icons or lists. But you can also use Cover Flow, the same system Apple uses in iTunes and on the iPhone to display album covers for music. In Leopard, a large preview of each file you select appears above the list of files in a folder, and you can rapidly scroll through these icons. These previews are live, and their contents can be viewed without opening the program that is normally needed to display them.

Time Machine backs up files.

For instance, if the file is a video, you can just click on it, and it will play. If it’s a multipage PDF file, you can click on it, and arrows will appear allowing you to flip through the pages.

An even better and deeper look can be obtained using a feature called Quick Look. Just hit the space bar or click on a toolbar icon, and a preview of any selected file zooms out. You can even view multiple sheets in an Excel file via Quick Look without launching Excel.

Another quick new way to see your files is available in the Dock, the Mac’s equivalent of the Windows Task Bar. Here, any folder you place on the right side of the dock will display its contents, after a single click, either as a grid of icons displaying miniversions of the file or as a “fan,” or arc, of such icons. These special Dock folders are called “Stacks.” Leopard includes one by default that is the destination for everything you download from the Internet, so your desktop will no longer get cluttered with downloads,

Time Machine: This built-in feature will continuously back up all of the contents of your Mac to either an external hard drive directly connected to the computer, or to a hard disk connected to another Mac running Leopard that’s on your network. The initial backup, in my tests, took all night, but after that, the system updates the backups hourly and I didn’t notice any slowdown during the process.

To recover any file you deleted, you simply click on the Time Machine icon, and you are taken to a view that shows file folders — or your email or address book or photo collection — in a stack of windows that appear to go on infinitely. You click on an arrow and the stack of windows zooms until you arrive at the last view in which the missing file existed. Then, you click “restore,” and the file is recovered in your normal desktop view. You can also restore whole folders, groups of files, or even an entire hard disk.

Shared computers: In Leopard, any computer that has been set to be shared on your network shows up on the left side of every Finder window. Click on it, and you can access whatever folders have been shared on those machines. Depending on the remote computer’s security settings, you may first have to enter a user name and password. It’s the simplest method I’ve ever seen for accessing other computers on a network. And it works with Windows PCs as well as Macs. When I first turned on the Leopard laptop in my office, it immediately found a shared folder on my colleague’s old Dell running Windows XP. She hadn’t even remembered sharing the folder, which contained files from 2003.

You can copy or move files to and from these shared computers, or view their contents with Cover Flow and Quick Look, or open them in programs on your own computer.

If you are a member of Apple’s optional .Mac service, which costs $100 a year, you can use a feature called “Back to My Mac,” which can access your Macs from thousands of miles away over the Internet. However, this feature works only over certain kinds of routers (not all of them Apple’s) and, as my router didn’t qualify, I couldn’t test it.

Remote control: For any Mac in your shared-computers list for which you have permission, you can take over the screen by simply clicking on a button called “Share Screen.” You can also remotely control distant Macs over the Internet using Apple’s built-in iChat instant messaging program, as long as you have permission and the Macs are running Leopard.

Stacks displays the files in folders in the dock.

iChat: Apple now allows you to use its instant messaging program with Google Talk as well as AOL’s AIM service, and you can set up a video chat in which you can present a slide show or display a document. You can also add special backgrounds that can make it look as though you’re someplace else, like Paris. In my tests, this even worked with someone on the other end using a Windows XP computer running the latest version of AIM.

Spaces: In order to cut down desktop clutter, Leopard lets you set up as many as 16 different desktops that can run simultaneously, with different programs open in each. You switch among these desktops by using keyboard commands or a menu.

For instance, you might have your iPhoto and iTunes running in one “space,” or desktop, your Web browser and email program in another, and Windows XP in another.

Leopard isn’t a must-have for current Mac owners, but it adds a lot of value. For new Mac buyers, it makes switching even more attractive.

Email me at mossberg@wsj.com. Find all my columns and videos online free at the new All Things Digital web site, http://walt.allthingsd.com.

In classrooms and offices, homes and coffee shops, Macs are far more visible in the U.S. than they were just a few years ago. Part of this success results from the fact that Macs are excellent machines that handle the most important and common tasks as well as — or better than — computers running Microsoft Windows.

But the new popularity of the Mac is also partly due to the fact that it can now run Windows along with Apple’s superior Mac OS X operating system. That means that if there’s a program you need that comes only in a Windows version, you can run it on any current Mac model, speedily and with all its features.

Starting next week, there will be a new way to do this. A company called VMWare, long the leader in what’s called “virtualization” — running multiple operating systems simultaneously on a single computer — will be selling a program called Fusion that allows Windows, and Windows programs, to run on a Mac.

I’ve been testing Fusion, and I’ve found it works well. For instance, as I write this column on a Mac laptop using the Mac version of Microsoft Word, Fusion is allowing me to simultaneously run several popular Windows programs — Microsoft Outlook, Windows Media Player and Internet Explorer. Each is running in its own window, just as if it were a native Mac program. I can switch from one to the other rapidly and smoothly. Their icons show up on the Mac’s “Dock,” just like the icons for Mac programs.

In my tests, Fusion never slowed down my MacBook Pro laptop or two other Macs on which I tested it. As I write this, the Mac version of Word and all three Windows programs are performing normally, even though I am also running five other Mac programs. My MacBook Pro, which isn’t the latest or most powerful model, has two gigabytes of memory and an Intel processor that is a generation behind the current model.

Fusion, which will be available for $80 at vmware.com, becomes the third major option for running Windows software on a Mac. It will go up against a fine program called Parallels Desktop, also available for $80 at parallels.com and at retail stores. The third option is Apple’s own Boot Camp, currently a free product available at apple.com/bootcamp. Boot Camp will become a built-in feature of the next version of Apple’s Mac OS X operating system, due in October.

All three programs require users to purchase a full version of Windows and install it on the Mac. Like Fusion, Parallels is a virtualization program that allows you to run Windows and Windows programs simultaneously with the Mac operating system and Mac programs. Boot Camp works differently: It requires that you restart the Mac to switch into Windows, and it runs only one of the operating systems at a time.

In my tests, I compared Fusion and Parallels, which is its closest competitor. I used Windows XP Professional. Each also works with the new Windows Vista (and with older versions of Windows and various versions of the Linux operating system). But Microsoft has imposed a legal prohibition on installing the most common consumer versions of Vista, Home Basic and Home Premium, via virtualization programs.

The two programs are very similar. In most scenarios, they function nearly identically. Both allow you to run the full Windows desktop either in a window on your Mac or in full-screen mode. Alternatively, both allow Windows programs to float on their own, with the Windows desktop hidden, so they look and feel just like Mac programs. Both permit you to fetch and save files from folders already on your Mac. Both support copying and pasting between Mac and Windows programs. Both automatically use your Mac’s Internet connection.

Parallels has more features than Fusion. It comes with a set of utilities Fusion lacks, such as a program that can migrate the contents of a physical Windows PC into a Parallels virtual Windows PC, and another that allows you to retrieve files from the virtual Windows machine even when Parallels isn’t running. Parallels also has a nice feature that lets you assign any file to automatically open in a Windows program instead of a Mac program. And it makes it much easier to use a printer over a network than Fusion does.

But I found Fusion puts less strain on the computer overall. While I like Parallels and have used it since it came out, it sometimes slows down my Mac, especially when it is starting up Windows or performing some other major task. Fusion has a much smaller impact on the Mac’s overall performance.

You won’t go wrong with either program. Both give the Macintosh a level of versatility that can’t be matched by Windows-only machines.

• Email me at mossberg@wsj.com. Find all my columns and videos online free at the new All Things Digital Web site, http://walt.allthingsd.com.

But, there’s a big barrier for Windows users tempted to switch to the Mac: software. While there are thousands of programs for the Mac’s operating system, called OS X, potential Mac buyers often find they have one or two Windows programs they must use that have no Mac equivalent. These range from custom software required by their employers, to niche programs for specific industries or hobbies, to games.

Yesterday, Apple took a historic, and potentially huge, step to remove that obstacle to switching. It introduced free software that makes it easy to install and run Windows on the latest Mac models as a complement to the Mac operating system. With this new software, called Boot Camp, you can turn your Mac into a fast, full-fledged Windows computer for those occasions when you must run a Windows program. That makes the iMac, the Mac Mini and the MacBook Pro laptop the only computers in the world that allow mainstream users to run both operating systems at full speed.

I’ve been testing Windows on a new iMac for several days and except for a couple of trifling annoyances, it runs perfectly, just like a stand-alone Windows PC. I was able to install Boot Camp and Windows XP Pro on the Mac in under an hour. After that, I installed 15 Windows programs, most unavailable in Mac versions, and all ran properly.

In Windows mode, the iMac was blazingly fast — far faster than my two-year-old H-P Windows computer. And every function of Windows I tested, including Web browsing, email and music playback, ran flawlessly.

Each system rests in its own part of the Mac’s hard disk, and the two don’t interfere with one another or share viruses.

In fact, I wrote this column in Windows on the iMac, using the Windows version of Microsoft Word. And I emailed it to my editors using Outlook Express, the built-in email program in Windows. When I was done using Windows, I just restarted the Mac and the machine turned back into a regular Macintosh, running the Mac operating system and Mac software.

Boot Camp (downloadable at www.apple.com/macosx/bootcamp) allows you to “boot up,” or start up, the Mac in either operating system. You can designate which one gets loaded when the machine boots up. Or, by simply holding down the Option (or Alt) key while starting or restarting the computer, you get a screen showing icons for the two operating systems. Click on the Mac icon and the machine runs the Mac OS. Click on the Windows icon and it runs Windows.

Each operating system gets its own dedicated portion, or “partition,” of the Mac’s hard disk, so they don’t interfere with one another. Programs you install in each operating system, and files you create with them, are stored in the part of the hard disk devoted to that operating system.

All of this is possible because the latest Macs use the same Intel chips as Windows machines. Boot Camp runs only on these new Intel-based Macs, which have been available since January. Older Macs can also run Windows, in a fashion, but only via a clumsy Microsoft program that creates a painfully slow “virtual” Windows computer that can’t handle some demanding programs, like games. By contrast, with Boot Camp, the new Intel-based Macs can become true, fast, full-fledged Windows computers that are essentially identical to standard Windows computers, yet still retain the ability to operate as normal Macs.

It’s important to note that Apple isn’t abandoning its OS X operating system, or adopting Windows. The company says it won’t sell, preinstall, or support Windows. In fact, while Boot Camp is free Apple software, anyone using it must supply his own copy of Windows to install. Boot Camp is technically beta, or test, software. But in my tests, it operated exactly as advertised. It will be built into the next version of the Mac operating system, called Leopard, due early next year.

You can’t run both operating systems at the same time. Switching between the two requires you to restart the Mac; the operating system you’re not using is shut down. That makes switching a little slow, but it also means that each operating system runs like a separate computer, with full control of the hardware. This allows Windows to run at full speed and protects your Mac files from the effects of Windows viruses.

With Boot Camp, you could choose to run a Mac solely as a Windows machine, with good results. But Apple doesn’t expect many people to do this. Instead, it assumes Boot Camp users will still use the Mac operating system and Mac software 90% of the time, switching into Windows mode only to run a few Windows programs. Some customers may never use Windows on their Macs, and just see Boot Camp as a sort of insurance policy that allows them to switch to the Mac without fear that they’d lose future access to Windows programs.

Apple’s move is only the first in what will likely be a series of new programs that allow the Intel Macs to run Windows. Today, a small Virginia company called Parallels plans to release a beta version of its own software to run Windows on an Intel Mac. It’s called Parallels Workstation for OS X and will cost $49, plus the cost of Windows itself. Unlike Boot Camp, Parallels creates a “virtual machine” that simulates a Windows computer inside the Mac OS. I haven’t had a chance to test this product, but may do so in coming months.

Last month, two hackers caused a stir by posting online their own method for running Windows on the Intel Macs. But, unlike Boot Camp, it requires technical skills far beyond those of the average user, and it doesn’t enable all of the Mac’s key hardware in Windows.

Until now, subtle hardware differences between Mac and Windows made it impossible to simply buy a copy of Windows and install it in a Mac, even the new models using Intel chips. Apple’s Boot Camp allows Windows to overcome these hardware differences, and also includes “drivers” — hardware-enabling programs — so that Windows can work smoothly with Apple keyboards, video systems and networking hardware.

Because the Mac becomes a true Windows computer when in Windows mode, it is susceptible to all of the viruses and spyware that plague regular Windows machines, but not Macs running the Mac operating system. While these viruses can’t infect the Mac side of the machine, you do have to install antivirus and antispyware programs on the Windows side.

To install Windows on a Mac with Boot Camp, you first must upgrade to the latest version of Mac OS X and perform what’s called a “firmware update.” Both are easy.

Next, you download the Boot Camp program, and install it. Boot Camp first guides you through the process of burning a CD with driver software you will later install in Windows. Then, it lets you divide the hard disk into separate Mac and Windows partitions. Finally, it starts up your Windows installation disk.

After that, Windows installs itself as it would on any regular Windows PC. Once Windows is up and running, you insert the driver disk created with Boot Camp, and this disk automatically installs the drivers that allow Windows to control the hardware features of the Mac. For instance, on Macs, you eject CDs and DVDs using a keyboard key that Windows computers lack. Boot Camp tweaks Windows so this key works.

In my tests, this whole process took 57 minutes, of which 40 minutes was claimed by the Windows installation.

After I had Windows running, I browsed the Web and received and sent email, using both a wired and wireless connection. I installed and used an H-P DeskJet printer. I played a DVD. I used a USB thumb drive to transfer files to Windows. All worked well.

Next, I installed 11 Windows programs that aren’t available for the Mac. These included Microsoft Access, Outlook and Publisher; ACT!; Adobe Photoshop Album; Microsoft Money; Family Tree Maker; Microsoft Flight Simulator; Microsoft Age of Empires; AVG anti-virus; and Spyware Doctor.

I also installed the Windows versions of Microsoft Word, Excel and PowerPoint. And I installed the Windows version of Quicken. These four programs are available in Mac versions, but in the case of Quicken, the Windows version is much better. I used these 15 programs for anywhere from five minutes to a few hours, and all worked perfectly.

So what are the annoyances and caveats about running Windows on a Mac with Boot Camp?

You have to reset the clock every time you start Windows. Windows also kept asking me to install my printer every time it started, even though it was already installed. Apple says it is working on these issues.

Also, you must buy your own copy of Windows to install — a full version, not an upgrade, of Windows XP, Home or Pro, with “SP2″ included. The Home version costs around $199, the Pro version $299.

In addition, you must use a wired keyboard and mouse during installation. And the Windows side doesn’t work with Apple’s iSight cameras and some other peripherals. You also have to adjust to some differences in keyboard layout.

Finally, there’s one dangerous step in installing Windows. In one of the screens of the installation disk, where you are asked which hard-drive partition will be used for Windows, you must select “C.” If you choose wrong, you could obliterate your Mac operating system. I recommend downloading and printing out Apple’s Boot Camp Installation Guide, which has a picture of this screen.

But these are minor issues. All in all, Boot Camp works really well. Whether you want to run Mac or Windows programs, an Apple computer may be the only computer you’ll need.

• Email me at mossberg@wsj.com.