[The Real Slim Shady]

Well, I havent done it in windows... but why not just partition the drive, then when you go to install the OS's, install them each in their respective partitions?

Its what ive done with Linux. Ive got 3 Linux operating systems on my external usb drive, then a dual boot Win7/Linux on my laptop. When i boot to the USB drive grub displays all 5 operating systems to choose from. Dont see why that wouldnt work as well with Windows though. Same principles? unless Windows prevents you from installing to removable media?