You can certainly run virtual PC on an iBook. However, when you say "play games", the games you'll be able to play in virtual PC - on ANY platform, even a G5 - is very limited. There have been threads on this in the Gaming forum.
DOS games run pretty good on a G5. Probably an iBook will done fine also. Once the rumored Virtual PC 8 gives you native graphics support with DirectX then a high-end Mac should be able to play mostly any game over 4 years ago as well as a PC of that time period. Emulation is very difficult process with only software. It is a miracle that it can run Windows XP.