I have much experience with mac's os on pc hardware as well as windows on mac's.
First: According to Apple's license agreement (for their os), you can only install the software on an "apple branded" computer. Most people get around this by throwing an apple sticker on the machine and call it good. Whether this would hold up legally or not I'm not sure.
Second: Because mac's os was written to work with certain hardware drivers, having mac's os work with your pc hardware is very iffy (completely depends on the computer and your abilities). Some people have managed to get working drivers for everything on their pc, while others are still searching for ways to get their wireless card working, etc.
Third: Boot Camp is a good option for installing windows on an Intel Mac. This is NOT an emulator, but more of a bootloader with drivers for windows (xp or vista). Once you have it installed it runs natively, utilizing all hardware on your mac. The downside to this is having to reboot every time you want to switch operating systems. This is where parallels is a great option.
