The issue is those virtual buttons. They use up some of the pixels so in reality the usable resolution is less than 800x480. In case of Streetpilot, it expects full 800x480 but Android on your phone says no and pushes it out. Streetpilot in this thread is hard coded for 800x480 or higher resolution.

To try to make a mod, we first need to find out the usable resolution of your phone, basically 800x480 minus the virtual buttons.