As always, this is a general guide aimed at mainstream, nontechnical consumers who dwell on common tasks such as email, instant messaging and surfing the Web; managing and lightly editing photos, videos and music; and using basic office applications. It is not intended for heavy gamers, video producers or corporate buyers.

There’s a vast variety of laptop models, but this guide is meant to cover the most common types of laptops, those with screens from about 12 inches to 17 inches, and weights ranging from around 2.5 pounds to 7 pounds.

For this column, I’m not including the category of tiny machines now called netbooks, with screens under 10 inches. I am also ignoring the huge, heavy laptops with screens larger than 17 inches that are primarily aimed at gamers.

Even the remaining mainstream machines range wildly in price, from bargain-basement models at $350 to high-end ones that can top $3,000. In my experience, the top brands for technology and reliability are Apple and Lenovo’s ThinkPad line, but various models from Sony, Hewlett-Packard, Toshiba and Dell are also worth investigating.

So, here is a quick guide to the key factors you should consider when buying a laptop.

Size: If you are a constant traveler, think about the subnotebook models, which generally weigh 3 pounds or less. There are two types of these. The classic subnotebook has a small screen, 12 inches or less, and a cramped keyboard. This year, a new type emerged, with a full keyboard and a normal 13.3-inch screen packed into a thin, light body. There are two of these: the MacBook Air from Apple and the Lenovo ThinkPad X300. All subnotebooks are relatively costly, typically ranging from $1,500 to over $3,000.

If your laptop will mostly stay at home, the office, or in class, a 5-7 pound machine with a screen of either 13.3 inches or 15.4 inches is the best bet. A well-equipped model in this class is likely to run you between $800 and $1,200. Typical models in this class are the Dell Inspiron 1525, the HP dv6700 and the Apple MacBook.

Windows vs. Mac: This is the eternal question. In my view, Apple’s Leopard operating system is faster, better and far less prone to malicious software than Microsoft’s Vista operating system. And the Mac laptops also come with better built-in software. The $1,099 MacBook is a solid, fairly priced machine, and the $1,999 MacBook Pro is even better. Both also can run Windows.

But Windows laptops are often less expensive, tend to have a greater variety of ports and slots, and come in more styles and sizes.

Apple’s MacBook

Operating system: If you are buying a Windows laptop, be aware that Vista is slower than Windows XP, in my experience, and still has compatibility issues with add-on hardware and software. If you’d prefer to stick with XP, you will find that many fewer models are available with it. And Microsoft has decreed that after June 30, mainstream, name-brand laptops will no longer come pre-equipped with XP.

Video: I recommend getting an LED-powered screen, which is brighter and saves power. Also, if you are choosing Vista, or if you do a lot of converting video for use on portable devices, consider getting a laptop with a separate video card inside that has its own memory.

Memory: If you’re buying an Apple laptop, two gigabytes of memory is plenty. If you’re using Vista Home Premium, I’d consider three gigabytes for best performance.

Processor: Any dual-core processor will be fine. Don’t pay a penny extra for faster processor speed.

Storage: In a mainstream laptop that will be your main computer, look for a 160-gigabyte hard disk or larger. A new kind of storage, called SSD, or solid state disk, is now available. But it is still way too costly for most users, and at the moment is available only in smaller capacities.

Battery life: Many laptops today rarely spend time away from an electrical outlet. But if yours will, look for a battery life of at least three hours between charges.

Wireless: Make sure your new laptop has the new, faster “N” version of Wi-Fi built in. Many cheaper laptops don’t. You can also get a cellphone modem built in, but they are costly and carry a monthly fee. You can always add an external cellphone modem later.

Other features: A built-in camera and microphone can be quite useful, and so can a feature on some Windows machines that allows you to play music and videos without fully booting up the computer.

Don’t let yourself be swayed by sales pitches, or by fanaticism for or against Windows or the Mac. Think hard about how you use your computer and what your budget will allow, and stick to those priorities.

• 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.

Time Machine is a key selling point for Leopard and the Mac. It is more complete, and yet simpler, than the built-in backup feature in Vista Home Premium, the most popular home version of Windows.

But Time Machine has a major drawback: It works much better on desktop Macs than on laptop models. That’s because it’s primarily designed to operate with backup hard drives you connect directly to the computer. And it’s a pain to plug a backup drive into a laptop, which can move around the house. While Time Machine will work with a remote hard disk under certain circumstances, that option requires a second Mac running Leopard, a costly condition.

Now, Apple (AAPL) has attempted to fix the problem with an unusual new companion product called Time Capsule. This is a $299 stand-alone networked gadget that packs both a giant hard disk and a speedy Wi-Fi wireless router into one slender case. It just plugs into your existing home network, and any laptop within wireless range can connect to it. It can back up multiple computers.

Time Capsule is designed to seamlessly work with Leopard’s Time Machine. But it can also be used as a wireless Internet connection, and/or a remote hard drive, for manually storing and retrieving files by Windows PCs running either Vista or Windows XP, or by Macs running Apple’s older Tiger operating system. And you can also use it with certain other backup programs, such as the ones built into Windows XP or Tiger.

In my tests over the past week, Time Capsule worked well in all of these scenarios. However, Time Capsule isn’t meant to do as many different tasks as some other networked drives.

Apple stresses that Time Capsule is a limited, targeted device meant primarily for backup — especially with Time Machine — and as a wireless base station. Unlike some other networked storage devices, like Hewlett-Packard’s MediaSmart home server, Time Capsule doesn’t allow users to simultaneously stream music or videos to multiple PCs, to easily access its contents via the Web or to stream videos to TV sets.

The $299 Time Capsule model comes with a 500 gigabyte hard disk inside, and there’s also a $499 model with hard disk that can hold one terabyte of data, or roughly 1,000 gigabytes. Both models use the same “n” class of Wi-Fi, the fastest version with the longest range. Both also work with computers equipped with the older “g” and “b” versions of Wi-Fi.

You can buy networked hard disks in these sizes for less money and simply use them with your existing Wi-Fi router. However, Time Machine won’t work with them, according to Apple. The company says the only standalone networked hard disk Time Machine can use is Time Capsule.

In my tests, Time Capsule performed perfectly with Time Machine. It also was easily recognized by several of my Windows machines running Vista and Windows XP. On all of these machines, I was able to speedily access the Internet via Time Capsule. Time Capsule can be set up to either replace or supplement your existing Wi-Fi router.

All the machines, even the Windows ones, also could recognize the Time Capsule as a remote hard disk, and save files to it and retrieve files from it. For instance, I manually copied a song, a photo and a Word document from a Mac laptop running Leopard onto the Time Capsule. On a Dell running Vista, I then opened the Time Capsule and launched that same Word document in the Windows version of Word, opened the photo in Vista’s Photo Gallery program, and played the song in Windows Media Player. This same process worked in reverse.

Apple doesn’t guarantee that Time Capsule will work with all backup programs. But it says it will work with the backup software built into Tiger and will likely work with some other backup software.

In my tests, the built-in backup program in Windows XP Pro worked fine with Time Capsule. But the built-in backup program in Vista failed. Microsoft said the problem I encountered was due to a new Vista security feature for backups that foils some remote hard disks, not just Apple’s.

Setting up Time Capsule was easy, using a step-by-step utility program that Apple supplies in both Mac and Windows versions. The device has a USB port that can be used to add either an additional hard disk or a networked printer. And it can be connected to a network via a wired connection if you don’t want to use its wireless functionality.

If you use Time Machine on a Mac laptop, then Time Capsule’s $299 price is money well spent. If you don’t, there are cheaper or more versatile solutions to the backup problem.

• 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.

Back in January, when I reviewed the massive new operating system, which took more than five years to develop, I called it “unexciting” because many of the breakthrough features Microsoft had planned for it had been jettisoned, and most of the rest were already present in the rival Apple Macintosh operating system, OS X.

But I also said it was “worthy,” and better than prior versions of Windows, because it has a stronger security system under the hood and better integrated searching.

Over the ensuing months, however, Vista has proved to be a disappointment, even though Microsoft says it’s selling like hotcakes. Based on my own experience and on reports from readers, it’s clear that many Vista PCs start up more slowly than new PCs running its predecessor, Windows XP, or than even well-worn Macs. And there is still a significant compatibility problem: Too many software and hardware products still don’t run, or don’t run properly, with Vista.

So, if you’re shopping for a new Windows computer, one of your first decisions is whether you want to get Vista, which comes on almost all new models, or to stick with Windows XP. PC makers are still offering XP on a few new consumer PCs. For instance, Dell offers four consumer laptops and two consumer desktops that can be ordered with XP.

Buying XP will likely result in fewer frustrations in the short run. But buying Vista may be the better choice for the long run. Over time, more and more products will be released that are tailored to the new system.

Your other option is to shun the Windows dilemma and buy a Macintosh. I regard the Mac operating system as superior to Windows, and Apple embeds it in beautifully designed machines. Macs have been spared the plague of viruses and spyware that afflicts Windows, and have better built-in multimedia software.

But, if you’re thinking of buying a Mac, it makes sense to wait a few weeks or months to gauge the early reviews and user reactions to Apple’s own new version of its operating system, called Leopard, due out Oct. 26. After that date, Apple won’t build in the current version of OS X, called Tiger, on new machines.

Here are some tips if you’re shopping for a new Windows PC this fall. They apply to desktop PCs and to most mainstream laptops, though there are additional considerations, such as size and weight and battery life, for smaller laptops meant primarily for travel. As always, these recommendations are intended for average consumers doing average tasks, not for heavy gamers, video professionals, or corporate buyers.

Operating system: If you opt for Vista, the best choice for average consumers is a version called Home Premium, which includes all of the new graphics and multimedia features. Many low-end PCs have only a stripped-down version called Home Basic. Some people may need Vista Business, a version that can link to some kinds of corporate networks that the two Home varieties can’t. If your budget allows, you can get an expensive version called Ultimate that includes the features of both the Home and Business versions.

Junk software: Most Windows consumer models are stuffed with “craplets” — crippled trial versions of programs. They take up space and can slow down the machine. One way to avoid these is to buy a so-called business PC, like one of Dell’s new Vostro models. Dell also allows you to opt out of trial software, especially when ordering its pricier XPS models. Many other manufacturers make this hard or impossible, especially if you buy a PC at a retail store. But the stores may clean up a new PC for a fee.

Memory: Buy at least one gigabyte of memory for Home Basic and at least two gigabytes for all other Vista versions.

Video: Vista’s flashy graphical interface works best with a separate, or “discrete,” graphics card that has its own memory. Some “integrated” graphics systems work fine, too, but they claim some of your main memory via an approach called shared memory.

Processor: Any “dual-core” processor from Intel or AMD should be fine for Vista. Don’t worry about processor speed. Buying added memory does more for performance.

Hard drive: Don’t scrimp on storage space, unless you are absolutely certain you won’t be saving many photos, songs or videos. Even an average PC should come with 300 gigabytes of hard-disk space for a reasonable price.

Performance: If you’re shopping in a retail store, try to check the performance rating Microsoft builds into Vista. It’s available by clicking “Show more details” in Vista’s “Welcome Center” screen. If this rating is below 3.0 on a Home Premium model, avoid the computer. For best results, shoot for 3.5 or higher.

Price: You can get a bargain-basement computer for under $400. But, for a versatile Vista PC with Home Premium, two gigabytes of memory, discrete video, a large hard disk and a dual-core processor, you should expect to spend $800 or more.

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.

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.