I'm going to have to echo what James said.
The thing I attribute most to my success in AP Calc and AP Physics last year was studying with friends. Oftentimes, you find that you'll understand something that the other person doesn't, and vice versa.
Go figure that by teaching you end up learning a lot through the process.
Also, I agree with kstl99. As someone who's been through all of the college prep talks (aka anyone who was a senior in high school), if you show improvement, especially with a difficult course load, then that will be very impressive.
Combine that with good test scores and who knows what the limit is.