I just passed this exam and I wanted to add some feedback.
Know your abnormal psychology very well. Many questions center on therapy and evaluation of progress for individuals with these diagnoses, so it is very important knowledge for this exam.
I saw nursing theory questions on Linda Richards, Hildegard Peplau, Gerald Caplan, and Maxwell Jones.
Know how the advents of psychotropic medications and brain scan technology have changed the general model of treatment for the mentally ill.
Know group therapy inside and out. Many, many questions on how groups should be run.
Pay close attention to therapeutic responses and the reasonings behind them. Much of the test was situationally based where you need to know not only what to say, but how to say it.
I had a toddler food ritual behavior question pop up on my exam, which surprised me. Know the most common of these behaviors, just in case the question is actually part of the graded portion.
I prepared for this exam by reading the recommended 840 page text. I also bought a NCLEX test prep book called "Straight A's in Psychiatric Nursing," which I skimmed through. It came with a CD that had a 276 question practice exam that was especially helpful in teaching me situationally appropriate therapeutic responses.
Good luck!