A rare snowstorm that has covered the Seattle area with glazed sheets of ice since Monday turned Microsoft's campus into a ghost town on the eve of its big official launch of Windows Vista and Office 2007 today.

Seattle has been in the grip of an unusual cold spell that resulted in wet snow that immediately froze late on Monday, leaving roads slick, hundreds of cars abandoned and schools closed.

Microsoft employs 35,000 full-time workers, or about half of its global workforce, in the Seattle metropolitan area, along with 5,000 contract employees. Most work at its sprawling suburban Redmond, Washington, headquarters, which consists of more than 60 office buildings.

While Microsoft officially remained open to employees "campus is pretty dead", said Ron Markezich, Microsoft's chief information officer for IT operations. He estimated that fewer than one in 10 employees came in to work on Tuesday, and more than three-quarters of Microsoft's Seattle-area workers checked email and did other work from home. That did not create any problems, Markezich said.

"We did not have to bump up network capacity or add servers. It didn't even cross my radar screen," he said.

Markezich said employees, even those logging in from their home PCs without secure virtual private network access, should be able to access most of their files and applications on their computers at work. That's provided they left their work PCs running with Windows Vista turned on, Markezich said.

The Microsoft software launch takes place later today at the Nasdaq Stock Exchange in Manhattan.