I think this is a Very Interesting Video for "How to make Volumetric Clouds"

http://www.ofb.net/~eggplant/clouds/CloudsInGames_NinianeWang.mpg

cYa Sebastian

Tutorials:
[Blender]Terrain creation ENG/GER
[Blender]Low Poly Tree Modeling
[GIMP]Create a Texture for Terrains
CLICK HERE