Microsoft is planning to release another OS in 2009.
http://www.pcworld.com/article/152638/windows_7_release_date_october_2009.html
http://www.microsoft.com/windows/windows-7/default.aspx
At the same time they are still struggling to get their users migrated to Windows Vista.
[1]http://www.theinquirer.net/inquirer/news/130/1050130/xp-gets-another-stay-of-excecution
Even the Windows XP website is trying hard...
http://www.microsoft.com/windows/windows-xp/default.aspx
http://www.microsoft.com/windows/windows-xp/future.aspx
The carefully engineered support policy is some thing users should be well aware of since vendor can sell them Windows XP till May 30th 2009.
http://support.microsoft.com/gp/lifepolicy
However, after nearly two years of existent Windows Vista hasn't been able to push Windows XP out and now its successor is also coming out :-).
Overwhelmed with all these? I am not. Because I use Kubuntu :-).
http://www.kubuntu.org/