Don't put foam on the walls! Chances are you'll buy the cheap flamible stuff, your drunk room mate will come home from the bars, light up a cigarette, toss the match at the foam, and the entire building will burn to the ground. (Remember Great White in Road Island?) In my opinion you shouldn't do a damn thing to the dorm room. Chances are you have a bed and your room mate has a bed, plus a couple dressers, a mini fridge, and a tv on a small stand, all crammed into a small room. That's more than enough stuff to absorb and diffuse sound and keep the standing waves down to a minimum. Wait until you graduate and buy a house to do any major changes to rooms. And when that time comes, buy some good quality studio foam.