I remember there was a thread once about sex education but I can't find it. I have a few years before I have to worry about this for my son but I found a wonderful video demonstrating condom use on an intact penis (not graphic - it uses a dildo and a paper towel). I know I personally had a lot of questions and this cleared it up for me. I think this is a wonderful video to show intact pubescent boys especially since most condom instructions/demonstrations either ignore or diminish the foreskin.
Video was uploaded by the video maker: http://www.youtube.com/watch?v=UOfbHI1Elbo