Citigroup plans to upgrade as many as 500,000 PCs to Windows Vista in the next 13 to 14 months, according to Microsoft CEO Steve Ballmer.

Speaking at an IT Pro Townhall held on Microsoft's campus, Ballmer also dismissed reports that a large number of US government agencies have forbidden the move to Vista.

"Vista has certainly not been banned in many government departments," he said. "I'm involved in a number of accounts where I expect to see deals signed in the next couple of months.

"It's about the same as the corporate uptake" of Vista, Ballmer said. He then cited plans by Citigroup, a major US bank, to upgrade 500,000 computers to Vista.

Ballmer may be referring to not widely circulated information from the mid-January business launch of Vista in New York. During the event, a top Citigroup IT executive, Jagdish Rao, said the company plans to begin rolling out Vista "on a large scale" to its 350,000 desktop PCs, starting in July.

A Citigroup spokeswoman verified that the company plans to begin rolling out Vista this July to the desktop PCs of all 325,000 employees. She did not comment on how long the migration is expected to take, or whether Citigroup also plans to update its employees' laptops.

Citigroup is rolling out Vista even as it plans to lay off 17,000 workers and offshore more of its IT operations in order to save $10 billion over the next three years.

Microsoft, which plans to spend $500 million in 20 countries to market Windows Vista, has given seemingly conflicting predictions on Vista's closely watched uptake.

Microsoft said late last month that it had sold 20 million licences of Vista in its first month of general availability, putting it at more than double the pace of Windows XP. Ballmer has said he expects Vista to ship 90 million PCs this year.

At the same time, Ballmer has also dampened outside expectations, especially from Wall Street around Vista's uptake. Despite those bullish comments, Ballmer, in response to an audience member's question, also said: "I'm not arguing with the idea that it [Vista adoption] has not been fast, it's just not that much different" from other operating system releases.