You could install vmware converter on the physical machine and from time to time run a Physical to virtual conversion. This would give you a virtual copy when you needed it.
Another solution is to use Norton Ghost and image the physical machine to a USB for instance. At any time the image can be converted to a virtual machine, either vmware or MS Virtual PC (VMware is easier though). You could setup a schedule and do this on a regular basis, whatever changes on the physical would get replicated to the image and thus the virtual machine