As partly offtopic, I am not sure if you are aware, but it is possible to connect Garmin *aviation* GPS units to FS2004 using the GPSOut.dll library add-on available here:
http://www.schiratti.com/dowson.html - the gps needs to have the "Aviation IN" -protocol selected and it needs to be in "simulator mode" as well. It's the "AV400" switch in the configuration file if you wonder. A serial port cable is naturally needed.
It's a great help to be able to fly real scenarios at home using the simulator, while working the GPS unit. Much more fun and useful than using the built-in simulator mode of the GPS in my opinion.