Like John said, you can use Bootcamp that is already in your MacBook. One problem with Bootcamp is that you have to reboot to switch OS's, with a program like VMWARE Fusion or Parallels you can have both OS's open at the same time. oh and don't forget, you need a copy of XP or Vista. On my system I use VMWARE Fusion with an added screen, so I normally have OSX on one screen and XP on the other.