Question about Garmin 276c Chartplotter with propietary memo

I purchased a Garmin 276c GPSMAP. I understand that the memory cards are proprietary. My question is how do I send map images to it? My computer does not see the unit's drive configurations. There are no folders available to drop the the image files to.

Me and my mates exchange .gpx files for dirt bike trail rides. The other two fellows have City Navigator 2010.10. Does anyone have an unlocked version of this? If so, Can I install this through Mapsource? and, do I place the urared .img file into the program data/Garmin file and upload to the unit? do I need to rename it? I want to keep the 2011.10 version as well and don't want to lose it.

Any advice or help doing this would be appreciated.

You need Garmin MapSource to comunicate your PC with the GPSmap 276c. These software come with the drivers.