You're going to have two messed up computers soon.
Anyone got any ideas how I can get round this?
You should not jeopardize your Vista computer trying to install XP on another drive connected to it with the intent of putting the drive back where it came from once XP is installed on it..
Put the drive back in the computer it belongs in and describe the problems you are having installing XP on it.
Someone here will know what to do.