Hi Martin, I am a Podium user and I agree with Gaieus that you
should look to the Podium forum for help.
The issues you are experiencing sound render related not sketchup related.
When you post your question at the Podium forum give as much
info as possible
ie podium version your using, preset used, image of render, etc.
Also If you are new to podium, check out the lighting and other tutorials found
at the Podium forum.
Good luck, hope to see your post.
http://supodiumforum.websitetoolbox.com/
Paul