This quote makes me think you're not aware of the vast architectural differences between the Apple/IBM/Motorla PowerPC and Intel/AMD x86(-64) processors. Basically, these two families of processors use such a different architecture, that an operating system needs to be specifically written and compiled to run on either one or both. With Windows 2000, Microsoft stopped focusing on other architectures other than the Intel x86 family (MS only started working with ARM next to x86 fairly recently), which are used by a few companies like Intel, AMD, Transmeta, and VIA. On the other hand, from the early 90s to 2005, Apple used a completely different family of CPUs, the PowerPC line. In 2006, they switched to the same family as Microsoft, x86. Due to this, Windows XP cannot natively run on a PowerPC Mac.
Emulation such as Virtual PC is an option, but I must warn you that this is a very, very slow ordeal. Basically, your PowerPC CPU runs an x86 emulation layer, on which Windows XP would run. That emulation layer takes a LOT of CPU power, and then XP still needs to run on top of it. This can be really, really slow, especially on a G4 single core processor. I'd suggest getting a cheap second hand Windows XP laptop for whatever you need XP for, a decent one shouldn't be hard to find for well under $50, and will be way more pleasant to use.
