B.D.
I learned a trick on "Super Nanny"(of all places!) It worked well for me. Put your son into his bed, tuck him in, and then sit quietly outside his room without talking or making eye contact. When he gets up, put him back without saying anything or making eye contact. Continue until he finally stays in bed. It may take a while (the first night I sat outside my daughters room for over an hour and put a screaming child back into bed at least 30 times). The second night was easier, and after 3 or 4 nights, she got it. She pretty much stays in her bed now. Ocassionally I find her sleeping on the floor behind her door, but she doesn't come out of the room. It's worth a try...good luck!