You might try the Trinity Rescue CD. You can boot to it and it can run a virus scan. You need to have an internet connection (preferably wired) to use the virus scans, as it offers you a choice of virus scanners, then downloads the one you select, loads it in the RAM disk, and uses it.
I burned a copy of the CD for grins and giggles and used it to do a disk clean-up on my girlfriend's computer, but I didn't test the AV stuff because I was too lazy to wire the box up to the router.
Theoretically, you can use wireless also, but the instructions aren't real clear about how to connect to a security-enabled wireless network.
Trinity Rescue CD
I heard about on the Linux Outlaws podcast
, if memory serves me correctly.