Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
For some reason the icon doesn't work. Shift+3 does cycle a Garmin GPS.
Edit: I'm sure one of the great developers out there can explain how to make the icon link work properly.
You may want to check the panel config file - there may be a "Window" entry for the GPS, toward the top of the panel config file, but the window data itself may not be in the file farther down.
Apparently Mike has a third party GPS installed. The gauge line in the GPS section is calling for a GNS530. Just replace the gauge00 line with this:
gauge00=fs9gps!gps_500,0,0