My automatic updates just popped up with it. So it's an official release now.
Windows XP Service Pack 3 (SP3) is an update to Windows XP that addresses key feedback from our customers and is a cumulative update that includes all previously released updates for Windows XP, including security updates. Windows XP SP3 contains a small number of new updates and should not significantly change the Windows XP experience. After you install this item, you may have to restart your computer.
More information for this update can be found at http://support.microsoft.com/kb/936929