Microsoft is sounding the support warning bell a few months early for customers who are running Windows XP Service Pack (SP) 2, Vista (with no service packs applied) and Windows 2000.
On April 13, 2010, Windows Vista with no service packs installed will reach the end of support. End of support means there will be no more security updates for this version, though customers who are on SP1 or SP2 will continue to receive security updates and support.
On July 13, 2010, Windows XP SP2 and all versions of Windows 2000 also will reach the end-of-support milestone. In addition, Microsoft will be ending support for Windows Server 2000 and moving Windows Server 2003 from the Mainstream Support phase to the Extended Support phase. (Extended means security updates remain free, but all other support is paid.)
More information on the XP SP2 and Vista support deadlines is available on the TechNet site. More on the end-of-support plans for Windows 2000 and Server 2003 is available here.
Speaking of upcoming deadlines, next week is March 1. That means those users still running the Release Candidate (RC) test build of Windows 7 will start experiencing bi-hourly shutdowns as a reminder that they need to take some action before June 1, when the RC will be phased out completely.