Ok, well I live in a dorm room now, and I bought my fishie with me.
I used to have him in a tiny tank, and by tiny I mean less than one gallon.
When I moved to school, I got a one gallon tank with an undergravel filter. I didn't get a heater because I know that dorm rooms are hot, and the water would be the right temperature without the heater. If your dorm had air conditioning (which most don't), then get a heater. It IS a necessity.
My betta seems VERY happy in his one gallon tank. A 2.5 gallon or bigger tank is recommended, but because you live in a dorm with limited space, one gallon should be fine, you'll just have to do more water changes.
Personally, I do 50% water changes at least 2-3 times a week. As for feeding, I just went away this weekend. I fed him a little bit more than I usually do on friday, and I fed him as soon as I got back on sunday. Fasting your betta for a day is good for his digestive system anyway.
Bettas are good pets to have at college, they're generally easy to take care of, and they're always a good addition to the room.
I love my betta fish to the max, and I wouldn't trade him for the world.
Just make sure you cycle the tank before you put him in there!