My brother has a mb. He just bought a usb external hd. I want to install xp on there using bootcamp. I thought i would be able to just select it, and windows could just run off of the hd? Now that i went to install it, it wont let me install it on the drive, so i am guessing the easiest way would be to partition about 5gb of my internal hd for windows, and then what? I would also like to use about 30 gb for osx, so how would i do that?