I second (or third, or fourth) the AVG vote. I've been fixing some people's machines lately, and as far as I'm concerned, Norton and McAfee cause more problems than they solve. Amazingly, the free software is easier to use, less annoying, and less processor-intensive.
And good luck to you folks trying to uninstall the pay programs. Those things are a b#$&% to get off the computer.
All I know is that my roommate used to get viruses all the time, often knowing he was doing something that would result in getting one. He'd get so fed up with all the viruses he'd get that he would reformat about once every two months!! I built him a computer and simply put Ad-aware and AVG on it, and he's been running fine ever since.
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Matt