Windows XP Service Pack 3 Release Candidate 2 is available to the public. Specific registry settings will allow you to be offered SP3 via Windows Update. You can also choose to download standalone update packages.
Windows XP SP3 is a rollup that includes all previously released updates for Windows XP, including security updates, out-of-band releases, and hotfixes. It contains a small number of new updates, but should not significantly change the Windows XP experience.
Patches and updates
Service Pack 3 RC2
Product page: here