What are the rules when creating objects and bringing them into WED? No matter how I create objects..they seem to not be renderable in WED.

e.g. I create a simple terrain in MED and save it as MDL7 format. I went into WED and load entity..but then I can't compile..I get 'level has no geometry' nor can I apply texture to the terrain.

Any tips are greatly appreciated. Also if anyone can recommend me any terrain and tree programs that work well with A6 that would be great.

Thank you