How do I add terrains from an outside source like terragen or earthsculptor? I tried what I could find in forums but when trying to import from a pic the terrain does'nt show in MED.

Build a terrain with model editor and just assign it to your map.

Hiya.

Hit the manual. It's got a good description of how and what different 'terrain' types you can use and the pros/cons of them (re: block/brush based, heightmap/terrain based, or model based). From my experience, I'd go with the model version for maximum diversity.