I render in segments a lot of times like Rim Runner suggests ... I have the base scene with everthing set and saved and then I add parts and render them. Don't save. Add more ... I also have a set of markers set up in another scene to get position correct. One or two obects that the characters are interacting with. Put the people there, make sure they are the right size and in about the right position and then copy them into the main scene. Tweak position and render. Repeat over and over ... It is kind of a pain but does get results without killing the computer or others about you. I had to use that process for this scene. http://ghostofmacbeth.posermail.com/Tolkien.jpg