As much as a bookmark blog as anything else so I know where to find it. You may have seen the malicious software removal tool come down through WindowsUpdate/MicrosoftUpdate. What I didn't know was that a version with the latest updates is released on the second tuesday of every month, and can be run from a web-page here or downloaded and run more often.
The tool works for XP, 2000 and 2003. The KB describing the tool is 890830, also updated monthly, and if you are considering deploying the tool within your environment, you should read another KB article, 891716. This KB describes the mechanisms for deploying through WSUS, SMS and Group Policy. However, remember that this tool should be considered supplementary to another solution such as anti-virus. Lots of layers help though.