Microsoft will mark the end of an era this weekend as Bill Gates and Windows XP -- two icons of the company at its zenith -- head for the sunset. Can Redmond survive this transitional moment, or will June 30 be the day Microsoft died?That Gates and XP are exiting simultaneously is fitting. Both are poster children for a style of computing that is fading, literally, into the clouds. Both also represent a late '90s to mid-oughts Camelot period that Microsoft may never recapture.

In his various roles at Microsoft -- as CEO, chief software architect, and, lastly, chairman -- Gates championed a PC-centric view of computing in which the desktop was king and the operating system was the brains of the whole operation.

And under Gates, Microsoft utterly dominated personal computing with its DOS and Windows systems.

Windows XP was the best of the bunch.

Reliable, relatively secure, and easy to use, XP may go down in history as the last, best OS for the client-server world. XP does everything an OS needs to do to facilitate traditional, networked computing. Indeed, its utilitarian excellence left Microsoft with nowhere to go.

As a result, the failure of the widely maligned Vista OS was almost preordained. All of Vista's bells and whistles -- like the silly, Flip 3D interface -- are merely subtraction by addition to a Windows environment that didn't need any more tinkering.

As long as client-server was the dominant computing model, that is.

But its days are numbered. Moving forward, computing will be all about the Web as a platform for tapping applications and services. It's a scenario that's been dubbed cloud computing.

Fat OS's, like Vista, and even XP, are overkill when it comes to the cloud. Cloud computing is all about fat pipes and distributed processing power. Thin operating systems that quietly, and modestly, direct traffic while running in the background will be all that's required locally.

In cloud computing, operating systems will be judged like NBA refs. The best ones are the ones you forget are there.

That's why it's appropriate that Windows XP and Bill Gates are retiring at the same time. They embodied Microsoft at its peak -- when client-server computing ruled the earth. But that's so five years ago.

Now, Microsoft needs to move forward with new leadership and new technology that can move it into the clouds if it's to compete with Google and whatever else crawls out of Silicon Valley in the years ahead.

The problem: It doesn't look like Microsoft is heading skyward any time soon.

Steve Ballmer, the current CEO, says he plans to remain at the helm for another decade. Ballmer, like Gates, cut his teeth in the desktop world, so he may not be the man to lead Microsoft's Web efforts.

And early glimpses of Windows 7, the successor to Vista, indicate that it will be as big and bulky as Vista itself.

That's not good.

If Microsoft waits 10 years, or 5 or even 3, to embrace the cloud, the computing industry will have passed it by. If that happens, tech historians will peg June 30, when Bill Gates and Windows XP exited stage left, as the day Microsoft died.