Step 1: download and burn <a href="http://www.knopper.net/knoppix-mirrors/index-en.html">Knoppix</a> Live CD and burn it. Insert in the computer and boot from the CD.

Step 2 (if Knoppix doesn't come with an AV): Download <a href="http://www.f-prot.com/download/home_user/download_fplinux.html">F-prot</a> for linux, install and run.