T.,
It sounds like he might be a little scared of the process and this is normal, as change of any kind is tough for kids.
Start slow. Introduce books and videos that show him it's okay and not scary. Talk to him about how Mommy and Daddy use the potty. Does he have a potty chair or are you using the regular toilet? If he's got a smaller potty you might want to show him by having you and Dad sit with him. The diaper is a comfort and his safety net to the actual process. And, what will help is some guidance and patience.
My son is 3 YO and has been potty learned for the most part a few months before he turned 3, but it took me a while to get him to really know what HE needed to do. Now that he knows he is the owner of the process and I depend on him to tell me when he needs to go, it works...for the most part. There are still accidents and oops I pooed my pants moments, but I can't fault him for trying and making the effort.
I bought books and had them everywhere! A Potty for Me and Yes, Potty No, Potty are even a favorite today. I took him to buy underwear that he could pick out. We talked about the pull-ups being a thing of the past, and now that he was a big boy he got to wear unders. I also adopted a routine similar to his preschool, which includes potty checks every 30 minutes. We go to the potty and check to see if he has to go, we wipe and then I let him flush the toilet. Oh and Huggies has a great free DVD on their site and another one that I forget the name of. But, check Amazon.com for potty training supplies and stock up!
But honestly, get him used to the idea first and the apprehension of the bare bottom stuff and then tackle the routine. Baby steps (as silly as it sounds) are the best way to approach change. Don't worry about what age others had their kids taught to use the potty or how many think this is too late or a discipline issue. Just do what you know in your gut (and heart) will work and stick to it.