Bassplayinbiker, I hope it works out for you. I rode my bike to high school and enjoyed it.
I agree with the above mentioned tactic of riding to school anyway, and parking your bike in a prominent place like on a railing right outside the principal's office. One thing I would add is, LOCK YOUR BIKE UP SECURELY! I have had two bikes (one pretty nice one) stolen in the past year, and it is really really discouraging. So make sure you lock up in a safe place.
(My question: what right does the school have to tell you how to get to school??? If you want to take the school bus, then sure they can make rules for it, but outside of that, how do they have any authority over what you do when not at school or a school-sponsored activity. Anyone can answer this?)