It's all about the rewards. Find out what he wants/likes and save it ONLY for potty rewards. Rewards can be TV, time with someone, a phone call to someone special, food...the key is to reward him with what HE wants. You may want the reward to be raisins, but if he wants chocolate, that is what it has to be. You will have to reward him for sitting on the potty calmly for any time with pull ups on. Then once that is cool and calm. Make if for longer and longer (books and toys while he is sitting there, again special for that time), then reward him for sitting unclothed, again just sitting should be rewarded and praised. Take him again and again, every 1/2 hour or so. Then you reward him for doing anything (even a drop) in the potty, moving up incrementally to what you want. You may have to really hold out on what it is that he wants. I had to do that with my son, he would cry. I would say do you want your train? Oooh, this is such a lovely, fun, green, train and I would drive it and drive it. Then he would finally go into the bathroom (that is where we had to start), and stand calmly, then he would get his train, or truck or whatever. I kept a plastic tub of them on the back of the toilet so he could see them, but couldn't get into them without my help. We are still working, it is a slow and painful process. Good luck!!!
N.