Windows XP Service Pack 3 (SP3) was made available to Windows Server Update Services this morning, classified as a service pack. It includes previously released updates and hotfixes to Windows XP and creates a new baseline for servicing. For more information about what's changed and how to deploy, see the Windows XP Service Pack 3 Overview.
One thing you may be aware of, if you happen to be managing any clients running Microsoft Dynamics Retail Management System, is an incompatibility Microsoft Dynamics RMS has with Windows XP SP3. To address the problem, we’ve added a filter to help prevent Windows XP SP3 from being installed on clients managed by WSUS and will make a fix available soon (more info here).
WSUS Program Manager