When developing a Project Management Office keep in mind the following items:
PMO Need - Why are you setting up a PMO? What are the Pros and Cons?
Cultural Change - What barriers will there be to setting up PMO? How will the PMO overcome these barriers?
Organizational Assessment - What is the Project Management Maturity of your project managers and the organization?
Methodologies - What Methodoligies will you use in the PMO? Templates? Business Processes?
Resources - How many people will comprise the PMO staff and what are their roles and responsibilities?
Training - What type of training does the staff require? What type of training does the organization require to support the PMO?
Metrics - What type of metrics will the PMO be responsible for collecting?
Lines of Authority - Who runs the PMO and why?
PMO Type - What type of PMO are you going to setup? Strategic? Business Unit Focus? Project Control Office?
Executive Buy-In - How are you going to get your company executives to buy-in to and then support the PMO?
Setting up a PMO is a daunting challenge that all to often ends up in failure. If your organization is seriously considering starting up a PMO make sure they have done their homework.
There are several excellent books that will help you and your company setup and operate a successfull PMO.
Take a look at:
The Strategic Project Office - A Guide to Improving Organizational Performance - J. Kent Crawford
Advanced Project Portfolio Management and the PMO - Multiplying ROI at Warp Speed - Gerald I Kendall, PMP and Steven C. Rollins, PMP
One final thought, don't be afraid to bring in an outside consulting company to help you through the process of setting up your PMO. Most PMOs are shutdown within the first few years due to the lack of perceived value by senior executives.