I've had the Windows OneCare Live Beta CDs for some time but refused to install as they require one to remove on board anti-virus and firewall (Zone Alarm in my case).
Thanks for the other link.
Haven't seen this mentioned here so some of you might consider giving it a try.
It is still in BETA and is an on-demand service that gives you free PC health and security scans, but it does not offer the continuous protection, monitoring, and automated tune-up features that Windows OneCare does.
PS - Windows OneCare is about ready for public beta and if anyone is interested in being in the public beta you can request being in it at this link -