Jason Alexander points to a Microsoft press release and has some good comments on it...
Microsoft to Acquire Enterprise Anti-Virus Security Provider Sybari Software
I'd love to see an Anti-Virus from Microsoft, as long as they make it as useful and easy to use as their Anti Spyware software. It would be even better to see both of these items packaged together into a single app, or "suite" of apps at least. I also hope that they continue to be free! Like Jason said, i'm tired of shelling out the big $ to be virus free.