G.L.
I have four children. Our 3 year old is the 3rd and so far the easiest to toilet train. I TRULY believe this is because he has had better examples! You have to lose all the pride and embarrassment and confront those icky bodily functions straight on. SHOW HIM that everybody does it. It is normal. AND NOTHING TO BE AFRAID OF. My three year old was also hesitant to "put his poops in the potty chair" instead of his diaper or big boys. I think he was afraid of "it". We talked about it, read all of our kid friendly toilet training books. Watched Bear in the Big Blue House (a special dvd on toilet training). And we made sure he witnessed that we all have this "function" every day. Finally, one day he asked for privacy .... and we praised him with high fives, "that is awesome", "I am soooo proud of you" .....but no loud jumping or screaming so as not to take the risk of frightening him in ANY way.
Patience and only positive comments. It will happen.
Also ... The Love and Logic series of parenting books have great ideas for encouraging the use of the toilet. Worth a look for many other reasons as well.