I used to use McAfee but had a lot of conflicts. I think the Norton suite with everything including is gfood choice.. Also pick up an external firewall/router thing.. Not that expensive.. Helps a lot
ZoneAlarm. The free version nags you at the start, but once you get it squared away it behaves itself. Plus, it lets you know if something already on your PC is trying to "phone home." Just don't freak out; use Google to see what it is before you shut it off.
(Did you know XP calls a Microsoft server to set your freakin' clock? Surprise, surprise.)
Solo Anti-virus has a pretty good shareware version. Even when the try is up it still work. It also defects and changes to your registry and and do you want to make those changes for good. That's really handy but it doesn't work after the trial.