Cannot find virus software for Win XP 64-bit

This should cover things for you: https://secure.avast.com/web/eng/x64.html

I have used Avast on 64-bit without problems, and am currently using Avira on a 64-bit system without problems. Kaspersky has worked for me in the past too.

Last I read, Avira was the most accurate.

You can try free anti-virus: Avast, Avira. But they r not that good. Or you may try: Kaspersky or Norton. They r pretty good, you can try trial for 30 days. Hmm, by the way Microsoft made a free anti-virus, it works on Windows only and if you have a genuine windows u can install it, it's called : "Microsoft Security Essentials"

Try AVG