Free avast! 4 Home Edition - Free antivirus software - free virus protection for home PC
Most of the user reviews that I read made the point that it's very user friendly, though PC World didn't like it and it's not recommended if you're using Zone Alarm. Then again, the new Norton said that it wouldn't work with Zone Alarm, but they seem to be playing well together on my machine. And best of all, it's free, so you might want to give it a try.