Hrmm... if I'm not mistaken, doing a low-level format will clear out a boot sector virus, though that is if you really want to do that...
--Mark
PS:
Though, if Norton and mcafee don't pick anything up and they are both updated, I doubt you have a virus, and making the claim that your mem is too low doesn't mean that you have a virus, any TSRs will lower the memory resulting in the situaion that you have.