To change the background (other than using a plane or other geometry) go to the rendering menu and choose environment. There you can edit the 'sky' colour, or put a picture (say of clouds). But if you're using Brazil then this might be slightly different, and I can't help in that scenario as I don't use Brazil.
Have you had a peek on dSRC's forums - they are very nice and helpful, and Ian.H has more experience with Brazil than me. I learnt a lot about LFS rendering there. Also Master Skinnerz has a forum devoted to rendering, and is popular with many of the great renderers here, so more help may be available (don't forget to search
).
Glad you're sticking with it. It's NOT easy this rendering malarky and it would be all to easy to give up.