From Microsoft Downloads
"Windows Defender is a free program that helps protect your computer against pop-ups, slow performance, and security threats caused by spyware and other unwanted software. It features Real-Time Protection, a monitoring system that recommends actions against spyware when it’s detected and minimizes interruptions and helps you stay productive. Now with 2 free support incidents for Windows XP and Windows Server 2003."
Don’t forget to check out my Windows Defender Preview at ActiveWin.com which I will be updating soon to reflect the changes in the final release.
Windows Defender for Windows XP and Server 2003 is finally here, after a two year beta, it’s been a long time coming for sure. Featuring a major over haul to the UI, Windows Defender is a culmination of months of hard work from both the Anti-Malware team and feedback from the community. Since January 2004, Windows Defender, formally named Windows AntiSpyware has been downloaded over 25 million times.