I've had a lot of roomates over the years through college and grad school, and the basic rule is that the new guy adapts to the house rules. You have to let them know, its just good manners. Its their house you're moving into, and even if you were paying rent, the idea is that the new roomie pretty much takes the house rules as is or doesn't move in, whether it be a ban on drugs, guns, pets or chore rotations. Second strong piece of advice, buy trigger locks. I like Master Locks because you can buy several that are keyed alike, and put them on everything. This is paramount, even if they are in a locked drawer or something. Your roomies may be fine folks. They will however, know at least one drunken idiot, its a law of nature. If he can't go "Hey, Dude, is this thing lo..BANG". Its worth the price of the locks.

Just my .02.
FQ13