A number of Windows versions are due their end of life cycle and as such all support for them will end soon, which means that there will be no more security updates. This means that the best option is to make sure you have the very latest Service Pack installed, or if possible migrate to the next newest version of Windows.
Windows 2000 Professional and Windows 2000 Server are approaching 10 years since their launch and both products will go out of support on July 13, 2010.
Windows XP was launched back in 2001. While support for the product will continue, Service Pack 2 will go out of support on July 13, 2010. From that date onwards, Microsoft will no longer support or provide free security updates for Windows XP SP2. Please install the free Service Pack 3 for Windows XP to have the most secure and supported Windows XP platform.
Finally, Windows Vista with no Service Packs installed will end support on April 13 2010. Please install the free Service Pack 2 for Windows Vista to have the most secure and supported Windows Vista platform.
Service Pack 3 for Windows XP:
Service Pack 2 for Windows Vista: