A lot of us have planes such as PMDG 737NG, PSS airbus, Flight1 Meridian. We have become accustomed to adding waypoints and such between airports.How do you do this in the flightplanning of the FS9 gps?

In the flight planner select the Departure and Destination airports. After selecting betwen VFR and IFR and betwen direct low altitude airways jet airways and VOR to VOR click the "find route" button. Then you can click the "Edit Route" tab to delete waypoints or drag, with the mouse, a section of the route line to the intersection or navigational beacon wou want to become part of your route. whatever route you pick will be loaded into the GPS and appear on the kneeboard (F10).Alternatively you could download and use one of several freeware or shareware flight planners.

I use FS Navigator 4 to build the flight plan, then export the plan to both FS9 and PMDG or NavData, depending on which aircraft I'm flying. If you choose to go this route, you'll need to get the export module for PMDG which is available in their "downloads/utilities" section.