Kae, the answers you have so far are fantastic. But let me remind you that there are no children in kindergarten who are still in diapers!!

He will do it all in his own time. The more you push, the harder he will fight. All you can do right now is SUGGEST, gently give potty ideas.
My son is now 4. Whe he turned 3, March 2005, I wanted to train also. Of course he was my 4th child so I already knew techniques. But guess what? He threw fits, similar to the ones you talk about.
I just started taking him in the bathroom with me and Dad took him also. We did not push nor did we put him on the potty, just brought him with us. Nothing was said afterward, just washed hands and left.
Eventually he trained himself by learning from example.
He will learn that it is uncomfortable to feel wet in the diaper or pull-up. Personally I do not believe in pull-ups because they are jusst like "big boy pants." They can wear them like pants and go in them and not feel wet. When he is maturing he will not want a diaper, my son said "diapers are for babies." And gave them up in a week.
The feeling of a full bladder or bowel is one of the hardest things young children have to learn. He may not have full knowledge or control of this yet.
He will eventually use the potty, the more you push him the harder it will be.
Just be gentle, let him do it on his own, when he does he will be more proud of himself and things will go smoother.