VirtualPC is a PC emulator, like a software PC. That means all that a real PC would do in hardware, VirtualPC does in the software. As such, it is of course by far less powerfull than a real PC, even on the fastest Mac (which the mini is not). Also, Virtual PC does not emulate DirectX, which is needed for most games.
That's why lots of people here have a PC as second setup, for gaming.