J., you need to watch Supernanny also. She, on many occasions, has addressed the issue of children not staying put in their own beds. I'll try to explain it, but you really must see when she takes this problem on in one of the shows. She has the parent put the child in his bed, then leaves the room and closes the door. Out comes the child! The parent walks to child back into bed, says NOTHING, tucks him in, and leaves the room, closing the door. Out comes the child again! Sometimes this will go on for 1 hour, and the parent is completely silent, while taking the child back into his bed, tucking him him and leaving the room. Eventually, it works. Really, it does. Like I said, you have to see it.
We never, ever allowed our twin daughters to sleep in our bed. Mainly, because we have a queen size bed and we are two large-sized adults and there simply was never room. Also, my husaband is an extremely restless sleeper, and with his size and constant moving of his 6'5" frame and 320 lbs, he would most certainly have rolled onto the child and crushed her. So, I'm glad we never had to deal with that issue, as many parents do after allowing their child in their beds.
Good luck. Watch Supernanny at 9pm on (I think) Tuesday or Wednesday nights - every week its on!