Starting early is great but don't get too ovewhelmed in studying for MCAT if it may mess up your undergrad GPA. A good GPA is just as important as a good MCAT score.
I agree with fishtolive that Princeton Review are good books. Kaplan is nice as well. In reality, all the prep books do at least a decent job of giving you information although their example tests may not be as close to the real MCAT as they could be.
Also, to get used to practicing for the reading comprehension section, you can use any GRE prep books (there are about a dozen of those out there). The Reading Comprehension section of the GRE is very similar to that of the MCAT. All it takes to do well on Reading Comprehension is to practice. You soon get used to the types of questions asked and more importantly how to pick the "best" answer. And, since the science sections of the MCAT are really just science-related reading comprehension sections, if you're good at reading comprehension you can ace the MCAT. Kudos on your early interest in the MCAT and good luck to you!
[This message has been edited by mpp (edited 02-06-2001).]