In principle it is possible to use a DEM map (gmapdem.img) on a Windows Computer.
I use a gmapdem.img for Europe from a Nuvi. Split it with GMaptool to a Mapsource installation (Windows registry).
Then You can use the map with Mapsource/Basecamp to make a track or route including elevation data. I use it sometimes for making tracks for my cyclingtrip through Europe.
There is a collection of DEM-maps on this forum. I cann't find the right link at the moment.
@Dustbike: DEM-map only contains elevation-data, no map-data. You can use it on a outdoor-gps. Disable the map, but the elevation-data is used in combination with other maps.