Virtual PC attempts to create an "emulated" or "virtual" PC completely through software. Vital components of a PC that don't exist on a Mac's motherboard are instead recreated in RAM. The drawback is that running a "virtual" chip in RAM is much slower than using a real chip.
There is no 3D video acceleration, since it would make the emulator completely useless in terms of speed. Even the fastest Mac emulating a PC equipped with only a 4MB SIS (?) video card will be lucky to achieve Pentium II speeds. Real world performance of Virtual PC is closer to a midrange Pentium I computer.
So while you might be able to play a few games using Virtual PC, most modern games using any type of 3D images won't work at all. The few games that do work, will run at a completely unusable (slow) speed.
Hope this helps!