Windows XP SP3 is continuing to progress through the development process towards release. I though you would find the following resource links useful in your planning/testing.
Windows XP Service Pack 3 (SP3) Release Candidate 2 (RC2)
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.
Get Windows XP Service Pack 3 Release Candidate 2
Download and deploy Windows XP Service Pack 3 RC2
This pre-release software is provided for testing purposes only. Microsoft does not recommend installing this software on primary or mission critical systems. Microsoft recommends that you have a backup of your data prior to installing any pre-release software.
Windows XP SP3: What is new and how to deploy
This white paper summarizes what is new in Windows XP SP3, and how to deploy the service pack