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.

So, here’s my annual spring buyer’s guide to desktop PCs. Most of what I say below also applies to laptops, although with laptops there are additional factors, such as size, weight, screen size and battery life. As always, these tips apply to mainstream users doing typical tasks, not hard-core gamers or techies.

Last fall, I advised average consumers with aging PCs to hang on until new Vista PCs emerged, rather than trying to upgrade existing models. I still believe that was the right course, because Windows upgrades are so tricky. But it turns out that even new Vista PCs have two big downsides.

First, Vista isn’t all that exciting a replacement for Windows XP. It’s much prettier and has much better searching, and Microsoft claims it has much stronger security, although you still need add-on security software.

Second, to an extent that amazes me, makers of Windows software and hardware have failed to update their products to work smoothly, or to work at all, with Vista. In my house, for example, the only built-in Vista printer driver I can find for my printer doesn’t allow the two-sided printing I can do with Windows XP and Apple Macintosh computers.

So, if you desperately need a new Windows PC, be prepared to be underwhelmed and to be frustrated by incompatible software and hardware. And if you’re not desperate, you might wait another six months or so for the software and hardware to catch up — and for Microsoft to issue some bug fixes.

Or you could buy a Mac instead. I still believe the best desktop computer on the market for mainstream, nontechnical consumers is the Apple iMac. It has gorgeous hardware and superior built-in software. Its operating system, Mac OS X, includes most of the key new features of Vista. And the iMac can even run Vista, along with its own operating system, if you need the occasional Windows program.

Apple has delayed until October the release of its new operating-system version, Leopard. But it’s almost certain that any Mac you buy now will upgrade to it smoothly. (See my Mossberg’s Mailbox for more details.) And the Mac is still largely free of the security problems that add such hassles to using a Windows PC.

But if you’re going for a Windows PC, here are my buying tips.

Vista Versions: The cheapest PCs will have only a stripped-down edition of Vista called Home Basic, which lacks Vista’s flashy new user interface. To get the full Vista experience, you’ll need more expensive machines that come with Home Premium, which also has more media features and is probably best for most average consumers.

If your company recommends it, you may need a different version of Vista called Vista Business, which lacks some of the media features, but can connect to some types of company networks that the Home versions can’t. Or you can buy a machine with the costliest version of Vista, called Ultimate, that includes all the features of the other versions. If you want to shun Vista altogether, you may still be able to find new PCs with Windows XP, though these machines may not be as secure as Vista models.

Memory: No matter what Microsoft or the PC makers say, I strongly suggest one gigabyte of memory, or RAM, for Home Basic, and two gigabytes for all other Vista versions.

Video: Vista Home Premium, Business and Ultimate will work best on machines with a separate, or “discrete,” graphics card with dedicated video memory. Some integrated graphics systems — built into the computer’s main circuitry — will also work, though they will drain some of your main memory through a scheme called shared memory.

Processor: For Home Basic, any current Intel or AMD processor in a new brand-name PC will work. For other versions, I suggest a “dual core” processor, like Intel’s Core 2 Duo, or AMD’s Athlon 64 X2, which pack the equivalent of two chips into one. Even if your processor can handle so-called 64-bit software, average users won’t find that capability useful today.

Hard drive: If you’re not much interested in video, music or photos, 80 or 100 gigabytes should be sufficient. If you are, 250 gigabytes or more is best.

Disks: Don’t buy one of the competing new high-definition disk drives, Blu-ray or HD-DVD, until the war between these competing formats is settled. Stick with plain old DVD.

Junky software: Nearly all Windows PCs are packed with “craplets” — the useless, annoying trial versions of programs. In a retail store, they may remove these for you for a small fee.

Price: You can get a bargain, brand-name desktop with Home Basic and a slow processor for under $400. But for a versatile desktop with two gigabytes of memory, discrete video, a large hard disk and a dual-core processor, you can easily spend $800 or more, without a monitor.

Just don’t buy more, or less, machine than you need.

Email me at mossberg@wsj.com.

Vista is much prettier than previous versions of Windows. Its icons look better, windows have translucent borders, and items in the taskbar and in folders can display little previews of what they contain. Security is supposedly vastly better; there are some new free, included programs; and fast, universal search is now built in. There are hundreds of other, smaller, improvements and additions throughout the system, including parental controls and even a slicker version of Solitaire.

After months of testing Vista on multiple computers, new and old, I believe it is the best version of Windows that Microsoft has produced. However, while navigation has been improved, Vista isn’t a breakthrough in ease of use. Overall, it works pretty much the same way as Windows XP. Windows hasn’t been given nearly as radical an overhaul as Microsoft just applied to its other big product, Office.

Vista’s Flip 3D feature lets you scroll through images of currently running programs. The sidebar (right) contains miniapplications. The Windows Photo Gallery (left) is for organizing and editing photos.

Nearly all of the major, visible new features in Vista are already available in Apple’s operating system, called Mac OS X, which came out in 2001 and received its last major upgrade in 2005. And Apple is about to leap ahead again with a new version of OS X, called Leopard, due this spring.

There are some big downsides to this new version of Windows. To get the full benefits of Vista, especially the new look and user interface, which is called Aero, you will need a hefty new computer, or a hefty one that you purchased fairly recently. The vast majority of existing Windows PCs won’t be able to use all of Vista’s features without major hardware upgrades. They will be able to run only a stripped-down version, and even then may run very slowly.

In fact, in my tests, some elements of Vista could be maddeningly slow even on new, well-configured computers.

Also, despite Vista’s claimed security improvements, you will still have to run, and keep updating, security programs, which can be annoying and burdensome. Microsoft has thrown in one such program free, but you will have to buy at least one more. That means that, while Vista has eased some of the burden on users imposed by the Windows security crisis, it will still force you to spend more time managing the computer than I believe people should have to devote.

Here’s a quick guide to the highlights of the new operating system.

Versions and Upgrading

Vista comes in six versions, two of which are primarily aimed at consumers. One, called Home Premium, is the one most consumers will want. It contains the full Aero interface, and it includes the functionality of Windows Media Center and Windows Tablet edition, which have been discontinued as separate products. Home Premium costs $239, or $159 if you are upgrading from an earlier version of Windows. It will come preloaded on most midrange and some high-end consumer PCs.

The other main consumer edition of Vista is the stripped-down version, called Home Basic. It includes the improved security and search but leaves out the new Aero interface and the Media Center and Tablet functions. It will be preloaded on low-price PCs. Home Basic will cost $199, or $100 for upgraders.

A third version, called Ultimate, will wrap up everything in Home Premium with some additional features from the business versions of Vista. This is for power users, and it is likely to be preloaded on high-end PCs. But some regular users may need Vista Ultimate if their companies have particular network configurations that make it impossible to connect to the company network from home with Home Basic or Home Premium. Vista Ultimate will cost $399, or $259 as an upgrade.

Even if you buy the Home Premium or Ultimate editions, Vista will revert to the Basic features if it detects that your machine is too wimpy to run the new user interface.

For most users who want Vista, I strongly recommend buying a new PC with the new operating system preloaded. I wouldn’t even consider trying to upgrade a computer older than 18 months, and even some of them may be unsuitable candidates. Microsoft offers a free, downloadable Upgrade Advisor program that can tell you how ready your XP machine is. It’s available at: microsoft.com/windowsvista/getready/upgradeadvisor.

If you bought a PC in the past few months, and it had a “Vista Capable” sticker on it, it should be able to run at least Home Basic. If it was labeled “Premium Ready,” it should be able to handle Premium and probably Ultimate.

Microsoft says that Home Basic can run on a PC with half a gigabyte of memory and that Premium and Ultimate will work on a PC with one gigabyte of memory. I strongly advise doubling those numbers. To get all the features of Vista, you should have two gigabytes of memory, far more than most people own.

Even more important is your graphics card, a component most people know little about. Home Basic can run on almost any graphics system. But Premium and Ultimate will need a powerful, modern graphics system to run well.

Performance

I tested Vista on three computers. On a new, top-of-the-line Hewlett-Packard laptop, with Vista preinstalled, it worked smoothly and quickly. It was a pleasure.

On a three-year-old H-P desktop, a Vista upgrade installed itself fine. But even though this computer had a full gigabyte of memory and what was once a high-end graphics card, Vista Ultimate reverted to the Basic user interface. And even then, it ran so slowly and unsteadily as to make the PC essentially unusable.

The third machine was a new, small Dell XPS M1210 laptop. In general, Vista ran smoothly and well on this Dell, but some operations were annoyingly slow, including creating a new message in the built-in Windows Mail program. This surprised me, because the Dell had two gigabytes of memory and a fast processor.

Security

Microsoft says Vista is much more secure than any other operating system. But this is hard to prove, especially at the beginning of its life, when few hackers and malefactors have access to it. One visible security feature asks for your permission before you do potentially dangerous tasks, like installing new software. This is a good thing, and it’s been on the Macintosh for years. But unlike the Mac version, the Vista version of this permission feature doesn’t necessarily require you to type in a password, so a stranger or a child using your PC could grant permission for something you yourself might not allow.

Vista also has built-in parental controls so you can restrict what a child can do on the computer. This is also already on the Macintosh, though the Vista controls are more elaborate.

Microsoft includes a free antispyware program in Vista, called Windows Defender. But PC Magazine regards it as inferior to paid programs like Spy Sweeper and Spy Doctor. So you may want to buy one of these. You should also buy an antivirus program, which isn’t included.

User Interface

The new Aero interface is lovely, and it makes using a PC more pleasant and efficient. It apes some elements on the Macintosh but retains a distinct look and feel. Icons of folders look three dimensional, and they pop. Most file icons are thumbnails that show a tiny preview of the underlying document.

Like the rest of Vista, the Start Menu has a prettier, more refined look.

The old hourglass icon that appeared during delays has been replaced by a gleaming, spinning blue circle. The cutesy names for standard folders, like “My Pictures,” have been changed to simpler ones, like “Pictures.”

As on the Mac, you can now drag favorite folders into a list at the left of open windows, so it’s easy to get to them.

A new feature called Flip 3D shows a 3D view of all the programs you’re running and lets you scroll through them. It’s like the Mac’s excellent Exposé feature, though not quite as handy.

Another new feature, called the Sidebar, is a vertical strip at the side of the screen that can contain tiny programs, called Gadgets, displaying things like favorite photos, news headlines, stock prices and the weather. Once again, this is awfully similar to a Macintosh feature called Dashboard, which displays tiny programs called Widgets.

Some familiar Windows features have new names. The old Display control panel, where you chose screen savers and desktop pictures, is now called Personalization. The Add or Remove Programs control panel is now called Programs and Features.

Search

Like the Mac, Windows now has rapid, universal, built-in search, a very welcome thing. The main search box is contained at the bottom of the Start menu, and it works well. Other search boxes appear in every open window.

You can also save searches as virtual folders, which will keep collecting files that meet your search criteria. This is another feature introduced earlier by Apple.

Built-In Programs

The Outlook Express email program has been given a face-lift and renamed Windows Mail. But it’s pretty much the same, except for a new junk-mail filter. The Windows Address Book has been renamed Windows Contacts and, oddly, turned into a sort of file folder.

The latest version of the Internet Explorer Web browser, with tabbed browsing, is included, though it’s also available for Windows XP.

As on the Mac, Windows now has a nice, centralized Calendar program. And there’s a new photo-organizing program, Windows Photo Gallery, but it’s inferior to Apple’s iPhoto because it doesn’t allow you to create photo books, or add music to slide shows. There’s also a pretty rudimentary DVD-burning program.

The familiar WordPad program can no longer open Microsoft Word files (ironically, Apple’s free built-in word processor does).

Gradually, all Windows computers will be Vista computers, and that’s a good thing, if only for security reasons. But you may want to keep your older Windows XP box around awhile longer, until you can afford new hardware that can handle Vista.

• Email me at mossberg@wsj.com.

I advise this delay because the Windows world is on the verge of an upheaval. Microsoft is about to replace its tired, insecure Windows XP operating system with the first all-new version of Windows in more than five years. It’s called Windows Vista, and it’s likely to be more secure and easier to use. But Vista won’t be available until around Jan. 30, 2007. So, all those brand-new Windows computers you might buy this holiday season will be powered by an operating system that is on its deathbed.

Of course, you can upgrade most new Windows XP computers you buy now to Windows Vista after January. And starting today, Microsoft and PC makers are offering an Express Upgrade program that will provide copies of Vista for free, or at reduced prices, to people who buy Windows XP machines bearing a “Vista Capable” sticker from now through mid-March.

The catch is that upgrading PCs to major new operating system releases can be a tricky business. Often, it works just fine, but in many cases there are significant problems. It’s always better to buy a new PC that has been matched at the factory with the latest operating system. Waiting just another 90 days could save you a lot of upgrading aggravation.

Also, the free or discounted upgrade program will, in most cases, entitle users of the common Home edition of Windows XP to obtain only a stripped-down version of Vista called Home Basic. That version lacks many of the coolest features of the Vista user interface.

What if you want an Apple Macintosh instead? Should you wait? After all, Apple is also planning an all-new version of its operating system, to be called Leopard, in 2007. I don’t advise Mac shoppers to wait, for several reasons. First, Leopard isn’t due until spring of 2007, months after Vista. Second, Leopard won’t be as disruptive an upgrade as Vista because it is the fifth major revision of Apple’s operating system since 2001, not the first. Third, because Apple makes both the hardware and software, Mac operating system upgrades tend to be relatively easy.

Apple isn’t offering holiday buyers any discounts or free upgrades to Leopard, but the company says all of its Mac models currently being sold will work fine with the new system. The current Mac operating system, called Tiger, already contains most of the key features promised for Windows Vista. I still regard the Apple iMac as the best consumer desktop computer on the market.

But, if you want a Windows desktop or laptop and you can’t wait until February for a model that is preloaded with Vista, here are some guidelines. As always, these tips are for typical mainstream users, not hard-core gamers or people doing intensive video production.

Vista compatibility: Make sure your new PC has a sticker that says “Vista Capable.” But this sticker guarantees that it will work with only the stripped-down Home Basic version of Vista. If you want to be able to upgrade to the Home Premium version of Vista, which has the full user interface and other features, or to several other versions of Vista, look for a computer designated “Premium Ready.” Naturally, these latter machines will cost more.

Memory: Microsoft suggests 512 megabytes of memory, or RAM, for the stripped-down Vista Home Basic, and 1 gigabyte of memory for full Vista. But I strongly suggest doubling those amounts. If you want to run Vista with all its features, get 2 gigabytes of memory.

Video: Vista Home Basic can run on any graphics hardware that can support a Microsoft technology called DirectX 9. This includes many “integrated” graphics systems, which don’t use a separate video card.

Vista Home Premium and other versions will work best with a separate, or “discrete,” graphics card that has at least 128 megabytes of dedicated video memory. Microsoft says even integrated graphics systems, like Intel’s chip sets labeled 945 or higher, will also work, as long as the computers containing them are labeled “Premium Ready.”

Processor: For stripped-down Vista, a processor running at 800 megahertz or faster should be sufficient, according to Microsoft. For full Vista, the speed rises to 1 gigahertz. For anything other than stripped-down Vista, I’d strongly suggest buying a so-called dual core processor, like Intel’s Core Duo or Core 2 Duo, which pack the equivalent of two chips into one.

Hard disk: Disk storage is already copious enough for Vista, and buying large amounts is inexpensive. For stripped-down Vista, I’d go for at least 60 gigabytes of hard-disk space. For full Vista, I’d boost that to 200 gigabytes, to accommodate lots of music and video.

Price: Don’t spend extra for a slightly faster processor. Invest in more memory instead. And factor in the cost of Vista. Even the Express Upgrade program may pay only part of the cost of an upgrade, which ranges from $99 to $259, depending on the version of Vista you want.

So, wait, if you can. But, if you must buy now, don’t scrimp on the specs.

• Email me at mossberg@wsj.com.