How long does Microsoft plan to keep selling copies of its Windows Vista operating system after the upcoming launch of Windows 7 (download)? The company isn’t saying. “We are still not sure if [computer makers] will be able to ship Vista once Windows 7 is made available. Having said that, an enterprise customer that purchases a PC with Windows 7 pre-installed is allowed to downgrade to Vista should they desire, similar to what we have today on Vista to XP,” wrote Richard Francis, general manager and Windows client business group lead at Microsoft Asia-Pacific, in an e-mail. Microsoft will stop supporting all versions of Vista in April 2012, Francis said.