NEW YORK (FORTUNE) - It has been a long slog for Longhorn, the code-name for Microsoft's next major version of the Windows operating system.

Now officially called Vista, the oft-delayed new version of Windows will appear sometime in 2006, Microsoft says. Microsoft's chairman, Bill Gates, is expected to offer more details in his keynote address Wednesday night at the Consumer Electronics Show in Las Vegas.

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Windows is the world's defacto PC operating system standard, but continuous and unrelenting security problems have made even Microsoft's most devoted corporate users more open to possible alternatives. At the same time, rival software companies, especially Google, are offering or will soon offer Web-based features and services that directly compete with Windows.

Vista, then, is critical to Microsoft's future. Microsoft says the various home and professional versions of Vista will offer vastly improved security against worms, viruses, spyware, adware, phishing and other Internet-borne attacks.

We'll have to wait to see if that's true. Woe unto Microsoft if Vista is not significantly more bulletproof and reliable than its predecessors. For physical security, Vista is expected to integrate support for biometric log-in (fingerprints readers and the like) and for user password verification (similar to what already exists in Apple's Mac OS X and Linux).

The long delay in bringing Vista to market -- the last major Windows revision, Windows XP, made its debut in 2001 -- has allowed rivals to beat Microsoft to market with core features. Vista will boast instant global (desktop and local network) search, cleverly called Search, but it will have to be significantly better than the current Google Desktop or Apple Spotlight to avoid being seen as a "me too" feature.

Microsoft says Vista will integrate seamlessly, or at least more easily, with multiple computers on a network, with smartphones, PDAs and other portable devices, and with home entertainment systems.

Cosmetically, Vista will look different from previous versions of Windows. The desktop (at least in versions I've seen) has a high-resolution, translucent, bottle-green graphical user interface called Aero, which shows off best on computers with advanced graphics cards. (Such cards ought to be standard when Vista-based PCs begin shipping in the fall, but if you're buying a PC or laptop before then, make the salesman promise it will fully support Vista Aero.)

Aero also offers better 3D effects, and improved document and application organization that is more flexible than the current file-and-folder hierarchy. Icons are dynamic, showing the first page of a document instead of just, well, an icon.

There will be scores of other changes in Vista, including support for DVD burning, HDTV and widescreen media, and podcasting (or "blogcasting," as Microsoft calls it).

As always, my advice is to sit out the first version of a major operating system revision, waiting for the inevitable Service Pack 1 (fixing the most egregious bugs that other, more impatient users have discovered).

Microsoft is expected to ship Vista to PC makers sometime around July or August, meaning Vista-based PCs should be on sale shortly after the back-to-school season, or at least in time for the 2006 holidays.

The arrival of Vista will also herald the arrival of a new, Vista-supporting version of Microsoft Office, the most popular suite of office applications.

Should you wait to buy a new PC until Vista is ready? Nah. Most PCs sold today should be able to run Vista out of the box when it arrives, and if not, upgrading a desktop PC is fairly simple.

Notebook and laptop computers, though, are a tougher call because of their limited graphics subsystems, which are difficult and expensive to upgrade. I'd advise getting a widescreen laptop with the best graphics you can afford, to make sure it's Vista-ready.

If you're thinking of buying an upgraded version of Microsoft Office, though, and don't have to upgrade right away, waiting for Office 12 (the Vista version) in the fall is probably a good idea.