Motard ??
Try turning on Receive Shadows from Surfaces in the Atmosphere Quality tab. This will keep the sun from shining through your objects.
I would also recommend to add a new Enviro Light and set it to Ambient Occlusion. When it is set properly, ambient occlusion makes a nice fill light. It will ass some depth to the objects.
Terragen 2 - it's not just for terrains anymore... :'(
lol^^ sure it is. Everyone needs a planet to stand on!