I bought Virtual PC 7 through my school yesterday (got a good discount), and installed it last night. I bought the version that doesn't come with Windows, and installed Windows 2000, which I had lying around from an old PC. Anyway, the installation was very straightforward. Just install VPC, start it up and insert the Windows installation disc. Then reboot the virtual PC so that it boots from the disk and follow the standard Windows installation procedure. No trouble to get it working at all.
I had worried about performance based on things I had read in these forums, but I find the performance very good on my 1.33 GHz 12" Powerbook. I'm using it to run PSpice and the Xilinx Verilog IDE (electrical engineering software), as well as to check web pages I design in Windows. It's obviously not as fast as a real PC, but the performance is perfectly acceptable.