"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 2 (RC2) of the SP2. Additionally, we have established 11 newsgroups for sharing information.
If you are only updating one machine, you should install the Windows XP SP2 RC2 via Windows Update. In most cases, your download time will be greatly shortened, and when you are done, you will also have the Release Candidate version of the Windows Update V5 client installed."