There is Boot Camp (download from the Apple site) that lets you choose Windows or OSX on startup and provides full use of your hardware.
VMWare's Fusion and Parallels are competitors in the virtualization business, letting you use Windows and OSX at the same time, but without much 3D
For Boot Camp all you need is a retail XP SP2 disk, and for the others all you need is a Windows disk. The step-by-step guides in the programs are easy to follow...