install raspbmc on a usb :(

[ViolentMonk]

I've been trying to figure out what I'm doing wrong but I don't know..I formatted my sdcard and installed raspbmc to it and ticked the install to usb and accepted the agreement. is having the usbstick in a powered hub okay? it all starts up fine and when it says that warning for 60 seconds afterwards it gives me some weird errors that fly by to quick and my resolution changes on its own so I cant see the border of the screen. also I'm using a model b and my usb drive is a 32gig lexar and a 4gig class 4 sdcard.