There is a distinct advantage to using VirtualPC in avoiding viruses... and other problems. Set it up to save your documents to the Mac HD instead of the PC Virtual HD. Then simply make a complete copy of the Virtual C: HD file when it is fresh and un-infested. Use the original C: drive file for your VirtualPC operations. DO NOT USE IT TO GET EMAIL OR FOR SURFING THE NET!!!
If it gets infested, delete it, make another copy from your back-up and off you go. Takes about two minutes.
I use the same technique in high risk environments. Virtual PC is a fantastic.