If I could make a suggestion, go to lynda.com and check out Chad Perkins "Essential Training" and "Beyond the Basics" series. Chad helped write the exam for Adobe, so would be the best guy to learn from. Plus, they're videos with exercises for you to try so you won't be buried in books.
He's awesome. It'll cost you something like $150 per course, but practice exams are like $125 anyways, so I'd rather learn the software than just how to answer exam questions.
He also does a series on Effects in AE, which is really good. I know all of this costs money, but if you're serious about learning, even if you're not going to take the exam, it's valuable to go through these videos to get an idea of what AE can do.
You'll also want to read your After Effects Help manual that came with the product. It's a really good document that goes over pretty much every aspect of AE.
All told, it might cost you $500 to learn about AE enough to write the exam, but it's worth it. It's a $1000 program, so I assume you'd want to get the most out of your investment, right?
Just my two cents. The alternative is buying sample exams.