Warren,
The test is difficult, but many people feel they overprepare for it. If you're scoring 60% or higher on the Simulator, you have a very good chance of passing the test. If you fail the first time, then try for some additional resources.
Literature, such as PMP for Dummies, should work just fine for your purposes. Also, supplement it with YouTube videos and podcasts.
However, if you're not currently struggling, there is no need for additional resources.