Haha never ever trust best buy. You go there and their geek squad will tell you they'll do a complimentary diagnostics, but I think they work on commision, so they do everything to get your money. Then when you have virus' they tell you that you need to give them $200 for a reformat or virus removal when you can reformat yourself.
(Reinstallation CD)
But yeah that sucks. I highly suggest getting AVG Total or whatever 2009 because it is AWESOME. Or get Kapersky anti virus, nothing should get you a virus. It's expensive but if you want I can always post it in premium for you.