Have you watched Supper Nanny? According to Jo Frost's Sleep Separation Technique:-
1. When you put your child to bed, give him a cuddle and tell him it's time to go to sleep, then sit very closely to he bed on the floor
2. Turn him so he's facing away from you. If he keeps eye contact with you, he will try to start a conversation. Tell him to close his eyes and that's it's time to sleep
3. Make sure lights off, and door open
4. Sit in silence, don't look at him. Each time he tries to talk to you, just tell him "Sleep", don't look at him.
5. The next night, repeat the same thing, but sit a little further away from the bed. Move further and further each night.
6. The last stage is sitting outside the room door, with the door ajar.
The technique is going to take a while, and will break your hear when he cries and screams. But remember, that you are breaking a habit that would otherwise go on for years.
Good Luck!