"It is only for downloading maps to your GPS"
Here you go from the help files of MapSource 5. 0. 1 Beta:
"Real Time Tracking and the GPS Tab
Tracks can be created in MapSource by connecting your GARMIN GPS to your computer and using the Real Time Tracking feature on the GPS Tab. Those tracks, and any tracks transferred to MapSource from a GPS will be listed in the Tracks Tab List.
When Real Time Tracking is enabled, MapSource reads information from the GPS,
shows the GPS as a red triangle on the Graphic Map, displays the tracking data in the GPS Tab, and records a track. "
MapSource is capable of a lot more than downloading maps. Software upgrades for your Garmin products are available
here.
As I type this I am running MapSource 5. 0. 1 Beta with my Garmin GPSmap 76S attached. The MapSource display shows my position as a red triangle on a map. I also have GPS information (lat/lon, speed, altitude, track, time, date, compass rose, & EPE) displayed along with the map.