Well, right now, I'm not using any anti-virus, but from past experience, Norton has some pretty good anti-virus apps, though I haven't treid then om Vista (I plan to get it soon). CA is one that you should stay away from, it caused problems for me and slowed down my computer a lot. ESET NOD32 ( http://www.eset.com/ ) is pretty good, it didn't slow down my computer, and seemed good. Windows OneCare has gotten bad reviews,mm but I haven't tried it yet.
So, for now, I reccomend ESET for now, but I'll tell you how the others are on vista (Symantec and OneCare).
Cheers,
Matt
btw, I was just wondering, comming from the mac, what do you think about Windows Vista?