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.