One thing I want to add is that some ISPs like Comcast and AT&T offer McAfee security Center to their subscribers for free. I think the same is true of other DSL and Cable internet providers across the country. Just food for thought.

In addition to antivirus you have to think of spyware. I have become a huge fan of SpyWareBlaster. Its free as long as you manually update it and it seems to be a good immunizer. I use that on my personal computers and all computers I fix and give the end user some nice simple instructions on how to update it or where to pay their $10 to get the autoupdates.