Windows XP SP3 includes previously released updates for the OS and also a small number of new updates. The current timeline for XP SP3 availability is as follows: Release to the Web (RTW) on April 29, 2008. Once released to the web, the final service pack will be available for download via Windows Update and the Microsoft Download Center. Automatic Update Distribution for users at home is scheduled for the early part of this summer
Obviously the release of a Service Pack is a significant milestone. There are some enhancements to Windows XP SP3 such as Network Access Protection (NAP) that will make it easier for enterprises to co-manage Windows XP and Windows Vista systems during their phased rollouts of Windows Vista. A couple of things to note when installing XP SP3 – if you installed on of the XP SP3 Release Candidate (RC) builds on your XP system, you will need to uninstall the RC build before installing the final version of the service pack.
Below is a table that outlines previously released functionality available to Windows XP in stand-alone updates. These features are included in XP SP3 by default.