Is XP still on the machine? If so, you need to boot from the XP CD. Then, it should ask if you want to install XP or repair a current installation with the Recovery Console. Choose install XP, press F8 at the agreement screen, and then it should ask if you want to install a fresh copy of XP, or repair the current installation. This time, repair, This is not the same as the prior repair request, as the RC is not used. You'll go through the same process as with a clean isntall, only it'll take half the time, and instead of starting from scratch, its going to replace the XP files already on your machine. This should take care of your booting problem. Once you get XP up again getting Vista off is relatively simple. I'll save that part for when you do get XP up.