I came with the same problem and resolved it... I didn't resolved the memory issue, but found that the main problem are the incredible high realistic textures...

My scene did not have to much things: a clothed Victoria 3 (several seperate clothes), a scene (The Ruins by Stonemason) and the VAP car by Sanctum Art. Even with the Maximum texture size set to 2048, i couldn't render it... And i have 2 GB of RAM.

The thing is that the background (in my scene the VAP car) don't need the texture size to be 2048 pixels. And the car has a lot of high resolution textures. The main problem is that you can't say in Poser that for this object, i want to use a maximum texture size of 512,

What you can do is resize the textures and use them... The memory usage will be reduced and you will be able to render your whole scene at once. This can be a long long work... That's why i made an application to do it "nearly" automatically (you must select which textures you want to reduce). The app is actually in beta testing... but will soon be available (for free, for WinXP with Framework 2.0).