Don't listen to peterockduke. He's just mad because he's starting to realize that saying he went to Duke for undergrad isn't going to be enough to carry him through life. Contrary to what he says in other threads, he does attack people personally, and that makes him a hypocrite.
Hard work and perseverence, rather than "talent", will be the primary determination of how you do in those classes. Talk to other students who have taken them before, find out how they studied, and find a method that suits you. Each one of the pre-reqs for med school have to be approached a little differently, but if you put in the time and effort you should be fine.