gantthead.com has some excellent materials regarding implementing a PMO - try a search on PMO.
Having implemented 7 global PMOs myself, I'd have to recommend finding a firm that specializes in it. The first company I worked at took three iterations and countless dollars. Had we hired professionals to start, it would have saved money and time in the long run. When I say professionals, don't hire just any consulting firm - make sure you talk to the companies that are most similiar to yours and see what they have to say about the experience and the consulting firm.
It's not just about knowing project management but really understanding the current environment and how your company's people best deal with change. You will want an assessment of the "as-is" with a recommendation and plan for how to get to the "to-be".
"There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
There is another theory which states that this has already happened."
