Character controller collider?

Hi everyone! Seems cool to find out the new Unity 4 Engine and new stuff! Anyway i'm here for one question that i never found an answer to by myself. Is there any way to manage the collision with a character controller through any type of collider? I mean, i wanted to create a race game where you obtain speed only if you pass through many circles. I've tought about it and i reached the solution that i have for any circle a plane that is inside of them. The problem is: how do i get the script (in c#) to have the collisions with that planes? Any attempt didn't work... OnCollisionEnter, OnTriggerEnter, nothing at all! Another question: is there another way to do that kind of "passing-through" thing? Thanks in advice!