Late reply but sounds to me like whoever did it knew the layout of your house to begin with, might be some one your room mates owed money to.
EDIT:
Do any of your room mates use drugs? An X Box is somthing easy to hock at a local game store for about $150, and that's enough to support a habbit for a day.
I don't see a professional crook going straight for an X Box in a house - like some are saying - with the whole knocking on the front door to see if anyone's home thing.
I still say it's some one who knows your house, and one of your room mates either owed them money or they're so cracked out on dope they were looking for a way to get a fix.
Real thieves ransack a house and throw everything into the center of a room, then deal with it from there.