http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/sp2predl.mspx

Microsoft has made Windows XP Service Pack 2 available as a "Technical Preview" meaning there is no support, so test at your own risk!

Windows XP Service Pack 2 (SP2) provides an enhanced security infrastructure that defends against viruses, worms and hackers, along with increased manageability and control for IT professionals and an improved experience for users.

To aid IT professionals in planning and testing for the deployment of Windows XP SP2, Microsoft is making available this preview, based on Release Candidate 1 of the SP2. Additionally, we have established 11 newsgroups for sharing information.

WARNING! This technical preview is unsupported and is intended for testing purposes only. Do not use in production environments.

Download here.

Thanks to Robert Haynie for bringing this to our attention!