It would seem that you have a too complex scene for a 32 bit system. Assuming you don't want to upgrade your system, I suggest either simplifying your scene or spliting it in several parts, render each one separately and merge them together in PS.
If you chose to simplify, the first thing to attack (because it's simple and because it's a real memory consumer) would be textures of Poser figures, if you have any. This has been treated in other threads in this forum. As to the rest, it depends on what else you have on your scene.