I had that condition when I was a kid. Basically, I wasn't really told by my parents proper hygien and as a result my foreskin became very tight and for months I was unable to pull it back. In despair and frustration, I eventually worked up the courage to slowly ease it back over a few days (bearing a great deal of pain), while applying mild antisceptic to the area.
I was eventually able to pull it back normally and I certainly learn my lesson. If you really think you can't pull it back, I would see a friendly doctor. But give it a shot... really you just need to bear a little pain and make the foreskin maluable again.
Hey bud, jump over to the male anatomy thread, I've just posted the answer to your problem. Your foreskin needs a bit of stretching and that should solve the problem, good luck!
Foreskin problem when erect 
