On April 13th, 2010, Windows Vista RTM will reach the end of support. And on July 13th, 2010, all versions of Windows 2000 and Windows XP SP2 will also reach the end of support.
Windows XP was launched in 2001 and Microsoft committed to providing a minimum of 10 years of support (5 years of Mainstream Support and 5 years of Extended Support) at the time it was released. In accordance with the policy, when Microsoft announced the updated release date of Windows Vista, it also provided additional 2 years Mainstream Support for Windows XP.
An unsupported version of Windows will no longer receive software updates from Windows Update. These include security updates that can help protect your PC from harmful viruses, spyware, and other malicious software, which can steal your personal information. Windows Update also installs the latest software updates to improve the reliability of Windows—new drivers for your hardware and more.
But even if you have an unsupported version of Windows XP or Windows Vista without any service packs, Windows will continue to start and run as usual.
Microsoft recommends those of you still on Windows XP SP2 to install the latest service pack available via the Microsoft Update website – Windows XP Service Pack 3 – or look at moving to Windows 7.
For more information on the end of support for these Windows releases, visit Microsoft for more details.
Additional Resource: Lifecycle Information for Windows.