He installed Vista first on C:\ then went and installed XP AFTERWARDS on D: so he lost the Vista bootloader. I haven't tried it, but on earlier discs, if you booted from DVD and went to advanced recovery options, you could chose automatically repair my installation. It could tell straight away that I had lost the bootloader and replaced it, whilst still being able to boot into XP too. For future reference: Because Vista is NEWER, always install vista AFTER you install XP, 2k3 etc.