My son is 2 1/2, and I have attempted starting potty training a little (he acts like he is ready, and has proven that he has control many times, he can go potty whenever he wants to), but he has no interest. He is still a year younger than your son, and I have not tried to force it, but he just doesn't even care. We tried underwear (I know people who had all their kids potty trained in a weekend at 18 months by putting underwear on and letting them be wet), but he didn't care. He was fine with wearing we underwear. I would sit him on the potty chair, and the times he was willing to sit there, he only sat for a second and refused to stay there, and then would pull up his underwear and go potty. The night before he had done great, and was using the potty chair really well. What I have noticed makes a difference for him, is if he is around other children who are potty training. I occasionally babysit a 3 1/2 yr old who is potty training, and every time we come home from his house, Connor wants to use his potty chair, and always goes potty when he tries. He gets excited from seeing other kids doing it too. The other thing that has worked great for him (only done twice) is going to Eden Prarie Center. The family bathrooms in the food court have a big toilet and a little one right by eachother. I was using the bathroom, and he sat on the "real" toilet his size and went potty at the same time. He was really excited he could go at the same time as me, in a real flushing toilet (not a potty chair). Then there is also a big sink, and one next to it lower for little kids, so we each had our own sink to wash hands. He gets really excited to go potty there, and every time something gets him excited about it, he will have a day or 2 at home of doing well too. Those are the only things that have gotten him interested so far. If you know of any other children you could set up a play date with that are potty training, if they go in the bathroom together and take turns, it usually gives them a lot more interest in it. I hope that helps a little!
J.