Vista + CA Antivirus = Bad
After installing Vista, I thought "Some sort of Vista specific Anti-Virus software might be a good idea.
I decided to try Computer Associates (CA) AntiVirus (AKA VET, AKA EZTrust)
I strongly suggest against it, as under Vista, I'd randomly get up to 60% usage of both my CPU cores, as well as only having 40mb (out of 2048mb!) RAM free.
Explorer will show up as having 50->60% CPU usage, but its actually CA's AV.
For now, I'm trying NOD32.
If speed is your thing, I recommend Antivir Personal from http://www.free-av.com . You can do auto updates, poke around in the scheduler section. Probably other settings would be good to change too. Or AVG, people seem to going on about that. Not really Vista-specific though.