Two months before Microsoft is supposed to finish Windows Vista, the first new version of its desktop operating system in half a decade, the company is under intense pressure to change not only the way it develops Windows in the future, but everything about it. The last big Windows shake-up was 10 years ago, when Microsoft integrated its Web browser and Internet Protocol stack to fend off Netscape. Now Microsoft is at a crossroads again, and whatever comes after Vista could be a radical break from the past.

While it's putting the finishing touches on Vista--a near-final test version could arrive this week--Microsoft is at work on the next major version of its most important product, a system code-named Vienna that's supposed to introduce a whole- sale reworking of the Windows desktop. Before that, a tune-up of Vista, dubbed Fiji, is in the works.

But post-Vista Windows will break with the past only if Microsoft can figure out how to do things differently. Here are the challenges the company faces as it works on Fiji, Vienna, and whatever follows them:

Faster delivery. First and foremost, Microsoft must figure out how to deliver Windows features faster. If it takes another five years to deliver the next major upgrade to Windows, Microsoft's golden goose is cooked.

More Web functions. Microsoft must increase the operating system's value by delivering many of its functions on the Web, in ways that can be updated as PC users' needs change. The Web can be a fabulous delivery vehicle for a modern operating system, but Windows has to get smarter about handling data and programs that live online. Windows Live and Office Live are part of the answer, but Windows itself needs to become Webified.

Better security. Windows' nagging reliability and security problems stem from its wide-open support of every software program and hardware device ever designed to work with the system. Microsoft must find a way around that.

Smaller Windows. The system has been growing with every version for the past 20 years. It's become so bloated with old code and features that the drawbacks (security holes, resource consumption, regulatory ire) outweigh the benefits.

	For Ray Ozzie, Microsoft's new chief software architect, no time to look back Photo by Ira Wyman/PictureDesk

Put another way, Vista could be the last whopping Windows operating system designed to run on a single PC, giving way to a sleeker design that divides functions across the PC and the Web. "Is Vista the last big release of Windows?" says Gartner analyst Tom Bittman. "I firmly believe that it is."

The stage is set for change at the company. Bill Gates said in June that he will ease out of day-to-day management over the next two years, and he's already relinquished many of his technical responsibilities as he devotes more time to his charitable foundation. Jim Allchin, the executive who has guided the technical direction of Windows since 1990, plans to retire in January. His influence already is on the wane.

Ray Ozzie, Microsoft's new chief software architect, has inherited many of Gates' responsibilities, and the future of Windows is now more in his hands than Gates'. Steven Sinofsky, brought onto the Vista project to get it out the door, recently took the reins on the follow-up to Vista. Sinofsky has a reputation for getting the company's army of programmers marching in the same direction, a sorely needed skill set in the Windows group.

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"The next version of Windows will be a transition from where Microsoft is to where it needs to be," says Rob Enderle, a principal at consulting company the Enderle Group. "Vista is our last operating system that looks backward." But that's only if Ozzie and his lieutenants can pull off a major overhaul. Most of the work still lies ahead.