Service pack 2 preview for Windows XP
http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/winxpsp2.mspx


This documentation has lots of information on the changes being made with the introduction of SP2. The page also contains a link to download the RC-1 version of SP2 (release candidate).

While I don't generally recommend installing beta service packs, RC-1 should be fairly safe. But even the finished one will undoubtedly have bugs, so install with caution! :)