The easily way to dual-boot Windows (XP and Vista) is to download and burn a Ubuntu CD. Download here. Then insert the disc into your computer while your run Windows. Click on Install Inside Windows. It will install Ubuntu Linux like a program and make it so you can boot from it even using a program called Rubi. Then chose your settings and recommend atleast 15GB for HD space and Install. If you decide you don't want Linux anymore just uninstall like any other Windows program.