Another trick I've heard about is to do things in segments. That is.. build part of your scene.. save the objects off, then remove them. Once your finished with placing all the objects and such.. load up the ones you removed. This final step will take a lot of resources.. but.. if you 'have' to model everything.. it will allow you to get them all in there. Then I suggest a nice long weekend somewhere while it renders.

The doctor says I have way too much blood in my caffeine system.