Despite its name, Virtual PC didn’t use modern virtualization techniques to make Windows work (the advent of Intel Macs is what made that possible). But it did let you run Windows on a Mac, albeit in a manner that was ultimately not all that satisfying. Parallels was the first application that did the job in a way that feels like you’re really running Windows rather than a fuzzy rough equivalent….

–Harry

http://en.wikipedia.org/wiki/Microsoft_Virtual_PC