Theres a fantastic book called Potty Training in 1 week, I think its by Gina Ford, not sure I'll have to check. It really worked for me full of loads of tips. My son was dry in 2 weeks.
My son 3 year old son would only wee when he was sitting on the loo. It was because he was frightened of falling down into the loo. I reasured him by holding onto him and at the same time I got him to put both his hands onto the seat behind himself so that he could hold himself upright.
