Back everything up regularly That way if you need to just clear everything off and start over you can
There are a few free ones, sorry though can't suggest any as I always use paid Try doing a search on a software site such as http://www.download.com or http://www.tucows.com
The best I found recently is avast www.avast.com Very good - It scans the machine during bootup before the virus gets a chance to get going.
The only problems I have with most virus protection devices is it hoses stuff like Alexa. I wasn't paying attention on one and clicked next and now my Alexa toolbar will not reinstall for anything.
You should be using firefox and search status... http://www.quirk.co.za/searchstatus/comments.php Much better than ie and the crappy alexa bar.
I've been using it. It doesn't send the data to alexa. I know that Alexa is useless, but some people still using it for advertising purposes in some niches.
One of the best is CA Computer Associates Nothing free will gve you proper protection from what I have found.. They are good at protecting you from the more simple virus but the real nasty ones will get by the free stuff. Also use a software firewall.
AVG is a good free virus protection program. The best way to avoid viruses is to avoid opening email attachments, and downloading files from untrusted sources. Common sense really.