The next update to Windows XP is now available for your testing. You can download Windows XP SP3 release candidate. The release candidate is not for mission critical systems, but rather for use in testing your software products. The service pack is to be available early in 2008. The release contains all of the updates since service pack 2, plus some other enhancements.
For example, SP3 includes a feature called Network Access Protection (NAP) that's borrowed from the newer Windows Vista operating system. NAP automatically validates a computer's "health," ensuring that it's free of bugs and viruses, before allowing it access to a network.