If you plug the product board into a PC's USB port, the first time it will not find a driver.  I have stored the driver .INF file in C:/Projects/Radio_Preflight/conf as at90usbxxx_cdv.inf so select this to configure the Windows driver.

If you look then in the Hardware Manager at the COM ports, you should see AT90USBxxx CDV USB to UART MGM (COMx) where x is the assigned COM port.   The only assignment I've seen is COM4.

There is a known issue with USB.  It works fine if you have it plugged in before starting the firmware, or plug it in after the firmware is running, but if you unplug it, then plug it back in, COM4 doesn't get set up properly. I have not yet determined if this is a PC or firmware issue. (June 11, 2010).

In order to proceed with coding the application without a working display or pushbuttons, I created a simple GUI simulator.  Once you open TerraTerm or HyperTerm, press capital D to enable the debugger. Then press lower h for help, and you will see the various keys that are active on the terminal to simulate pushbuttons as well as the display.