That Mac uses a PowerPC processor which is a completely incompatible architecture with the Intel one that is used in Macs since 2006. The only way to run Windows on it would be through a PC emulator such as Virtual PC (which is commercial software that you must pay for) or Q (which is open source and free).
Be forewarned that which ever one you choose, it won't be as fast as running Windows on a real PC. Emulation is almost always slower since you're emulating another computer architecture.