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.

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, formerly known by its code name of Longhorn, is due out about a year from now, well within the lifetime of any PC you purchase today. I assume most consumers running Windows will want to upgrade to Vista. Microsoft promises a host of new features, and says Vista will be much more secure than today’s Windows XP.

There’s a catch, however. Vista is Microsoft’s biggest upgrade to Windows in a decade, and it will require much beefier and costlier hardware than Windows XP. So you will have to rethink your PC buying assumptions, starting now.

Microsoft hasn’t published final hardware requirements for Vista yet, but I have been talking to the company about them, and feel comfortable that the specs I am recommending below will allow you to upgrade to Vista with confidence. Although this is a desktop guide, most of these recommendations apply to laptops, too.

If you don’t care about Vista, and plan to stay with Windows XP for the life of your next computer, follow my last desktop buyer’s guide, which ran in April and is still valid for XP. It’s available at: http://ptech.wsj.com/archive/ptech-20050407.html.

You also won’t have to worry about Vista if you buy one of Apple Computer’s Macintosh computers, which don’t run Windows. Every mainstream consumer doing typical tasks should consider the Mac. Its operating system, called Tiger, is better and much more secure than Windows XP, and already contains most of the key features promised for Vista.

Microsoft says Vista will automatically downgrade its features to match weaker hardware. Computers with marginal specs won’t be able to take advantage of all of Vista’s capabilities, and will retain the look and feel of XP.

So, I don’t recommend buying a low-end PC this fall and winter if you expect to upgrade to Vista. The new operating system will almost certainly be crippled on such a machine, or not work at all. Expect to spend $600 or more without a monitor, for a PC that can fully run Vista.

Here’s what that machine should contain:

Memory: It’s likely Microsoft will suggest 512 megabytes of memory, or RAM, for Vista, but companies almost always understate such requirements. I strongly recommend at least one gigabyte of memory. Microsoft officials privately agree that a gigabyte would work well.

Video: The new Windows will be especially dependent on strong video. Many low-cost and midlevel PCs today use something called integrated graphics chips, which are attached to the computer’s main circuit board and don’t have their own dedicated video memory, called Video RAM, or VRAM.

To make the most of Vista, you will need to shun this design and opt for a machine with “discrete” graphics — a video card that’s separate from the main board and has its own dedicated memory. Look for at least 64 megabytes of video RAM, preferably 128 megabytes. By next fall, integrated graphics chips may be good enough for Vista, but not today.

Processor: I have always recommended avoiding spending extra dollars for the fastest processor, and that position still holds for Vista. I wouldn’t buy a computer with the cheapest or slowest processor, but a midrange Intel Pentium or AMD Athlon processor should be fine. Consider a “dual-core” processor that essentially combines two chips for added speed and power, though it’s not a Vista requirement.

Another option worth considering is a processor capable of so-called 64-bit computing. This isn’t necessary for Vista, but it’s the wave of the future, and it will be much more powerful than today’s computing, which relies on 32-bit processors. There isn’t much software yet that takes advantage of 64-bit processors, but a lot more is likely to appear in Vista’s wake. An AMD Athlon 64 would be a good bet, because it can handle both 32-bit and 64-bit software. Intel makes similar processors, which have the term “EM64T” in their names.

To take full advantage of a 64-bit processor, you should also double the computer’s memory, to two gigabytes.

Hard disk: Disk storage is already copious enough for Vista, and buying large amounts is cheap. I’d go for at least 160 gigabytes of hard-disk space, because Vista will offer easier ways to manage and create video, which eats up hard-disk capacity. Also, I’d suggest making sure the hard drive is fast. It should run at 7,200 revolutions per minute (RPM) and have a cache of two megabytes.

DVD drive: Vista will have much improved DVD recording for storing videos and for data backup. So, I suggest you get a PC with a fast, multiformat DVD recording drive.

Next year, closer to Vista’s release date that fall, Microsoft will publish more-detailed specs for Vista-capable PCs, and I will make any refinements or additions needed to this list. But, if you buy a PC now with these specs, you should be in good shape for Vista.

• Email me at mossberg@wsj.com