Francesca:
It does seem overwhelming at the outset, but it is not.
I used a multi-level approach because of the way that I learn and because of where I judged myself compared to the PMI PMP Test Standard. I have a very auditory learning style, meaning I need to hear the information as opposed to reading it, so this approach may not work for you.
In conjunction with the PMPrepcast (essentially a lecture series on the PMBOK Guide), I purchased the book Head First PMP and of course, the PMBOK Guide. I followed the Prepcast along with the PMBOK, then circled back in Head First PMP. I then augmented that with 10-50 question quizzes from the Exam Simulator in each knowledge area. About 5 weeks into studying (and a little over half way through the PMBOK/Prepcast), I started full Exams from the simulator, recognizing that my scores would be terrible because of material that I had not yet covered. I repeated that process until I finished the Prepcast/PMBOK and Head First, then repeated exams and went through all the quiz questions. I also made a set of flash 49 flash cards with knowledge area/process group/ITTO information on it.
Like David, when you hit can consistently hit 80%+ on exams and quizzes, you know you're close to the end.
I did not "read" the PMBOK Guide but I did follow it with the Prepcast and took notes in my guide. The PMBOK reads like any other ANSI standard and has all the excitement of watching paint dry.
It's a lot of material, but 12 weeks of hard-core studying did the job for me. (Note, I'm an independent consultant so planned my time accordingly. You may not have that luxury).
Good luck!
Harry
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Harry J. Elston, Ph.D., CIH, PMP