The latest Service Pack for Windows XP, SP3, is now available for download. Of note in this release, Windows XP with Service Pack 3 will have the ability to be a NAP (Network Access Protection) client. Also, Wi-Fi Protected Access 2 (WPA2) support is now included (previously available as a separate download for Windows XP SP2).
Service Pack 3 Resources for IT Professionals (Microsoft TechNet)
How to obtain the latest Windows XP service pack (Microsoft KnowledgeBase)
List of fixes that are included in Windows XP Service Pack 3 (Microsoft KnowledgeBase)
Thanks to Boyd Benson for his assistance with this post.