Windows XP Service Pack 3 (SP3) was recently released as a critical update to Windows XP systems. This update is welcome in that there is still an investment in core updates with the popular operating system compared to Windows Vista, but it will probably be the last service pack style update with core feature additions. Among the network-related features is an update to the XP implementation of the Wi-Fi Protected Access 2 (WPA2) wireless networking standard. This update brings XP's wireless networking support up to the June 12, 2007, specification level of WPA2 at IEEE 802.11i, which focuses on wireless medium access control (MAC) and physical layer specifications.
Support for WPA2 started in 2005 to replace wired equivalent privacy (WEP) functionality, but it has not been updated since then with changes to the WPA2 standard. XP3 is defined as a critical update, and it may arrive on your network before a planned update is launched if your users use the Windows Update site independently. Among other networking updates, SP3 also gives formal support for Microsoft's network access protection implementation as well as simplified IPSec policy creation and maintenance.
The Windows XP SP3 overview document explaining the additional WPA2 support and other related features can be found at the Microsoft website.