How do I "sound proof" my room?

I live in the basement of a duplex. I live with two of my friends. I got the basement because I have severe insomnia, and the dark and quiet was supposed to help. The problem is-I hear EVERYTHING. The walls and floor are so thin that I hear my roommates walking around, shifting in their beds, flushing the toilet, running water, etc. Is there anything I can do to my ceiling and/or walls, that's inexpensive, to make all these noises quieter?