thanks so much for all of your replies.  though now i'm thinking about pictures that use a low flying frog.  :D   no, i didn't want a prop.  actually,  i have particles, so if i wanted unchanging texture driven fog, that's what i'd use.   i really want to  have pure material room fog, where i can change the turbulence and such without having to make a new texture.   i'm making some progress on my own, but it's still too harsh.