Some suggestions:

Terragen: There's a free version, works well and is relatively easy to figure out.
Use a background image:  There are plenty in freestuff and tons of free stock images online
for fire:  Me personally, I've never had a great experience creating fire in poser, however i've had some success with bryce 5.   If neither works for your purposes, you can find free images of fires online and take them into a paint program and make brushes out of them to add to the scene later.   For lighting of fires (and you can try it in poser) in freestuff is "ultimate fire", i've had some minor success with it.

Hope that helps