An increasing number of viruses/worms will not run if they detect the presence of a virtual machine (to discourage the development of signatures for it). Some antivirus researchers now advocate installing a fake virtual machine to protect a computer. I don't know exactly what this would involve, but it might be worth looking into for ClamWin. I believe the viruses only look for a few lines of code to mark the presence of a virtual machine.

Regards,

P.S. Some viruses also look for the presence of a debugger, so this might be possible to fake also.