Thought everyone knew VMWare? Alright here'* the run down:
Virtual Machine Ware -
VMware Virtualization Technology, Virtual Machine, Green IT Servers, Hypervisor - VMware
Basically you can run a different operating system within your own OS, it'* a program and you can let'* say if you have Vista Ultimate 64bit, and you want to run Windows XP, well download the ol' vmw and you can emulate XP in it'* own environment you don't have to switch anything! You can do it for 98, 96, etc. Supposedly you can play old legacy games on it. Well, in theory you can run Mac OSX on vista with VMware.
Or you can just call my brother up and he'll make your windows run like a mac, and I'll make it look like one too! We're nerds in that fashion hahaha.