Jan. 17 (Bloomberg) -- Microsoft Corp. Chief Executive Officer Steve Ballmer said sales of the company's Windows Vista software to businesses may exceed his initial estimates.

``We're very excited about where we are out of the chute with Windows Vista,'' Ballmer said today in an interview in New York. ``I expect to see uptake at a pretty good rate relative to my early expectations.''

Microsoft, the world's largest software maker, released Vista for corporate customers on Nov. 30 and plans to introduce the operating system for consumers on Jan. 30. The Redmond, Washington-based company is spending a record amount to market Vista, its first new version of Windows for personal computers in five years, in an effort to fuel revenue growth.

Citigroup Inc., the world's biggest financial-services company by market value, plans to start adding Vista to 350,000 desktop computers in June, said Ballmer, 50.

``Those kinds of proof-points just continue to make the case to other enterprises,'' Ballmer said.

In a November interview, Ballmer cautioned that analysts' surveys, some of which predicted only 20 percent of customers would begin upgrading to Vista in the first 12 months, were too conservative. He predicted ``significantly'' more customers would begin using Vista in the first year.

Sales are expected to pick up as Microsoft releases Vista broadly later this month and the new version of Office at the same time, Goldman Sachs Group Inc. analyst Rick Sherlund wrote in a note today. The two programs will generate additional revenue of about $1 billion over 12 months, he said.

Windows Sales

Microsoft shares lagged behind competitors' last year partly because of delays to Vista and concerns the program would be met with slow initial demand. The stock gained 14 percent last year, while Oracle Corp. rose 40 percent. Microsoft fell 6 cents to $31.10 at 4 p.m. New York time in Nasdaq Stock Market composite trading.

The Windows operating system runs almost 95 percent of the world's personal computers and generated $13.2 billion in revenue in the fiscal year ended June 30, accounting for about 30 percent of Microsoft's total sales. Windows' growth has trailed the overall PC market as Vista was repeatedly delayed.

Microsoft's digital music player, the Zune, made ``a very credible showing'' during the holiday season, Ballmer said. The Zune, priced at $249, competes against Apple Inc.'s iPod, which dominates the market. Zune went on sale Nov. 14 and Microsoft expects to sell more than one million devices by June 30.

To contact the reporter on this story: Brian Sullivan in New York at bsullivan@bloomberg.net

Last Updated: January 17, 2007 16:07 EST