Try reducing the bucket size to something small like 16 (MB), or less even, if it lets you.
You can try rendering the scene in smaller parts, and then adding them together in
gimp, or something. Right next to the render button, is render area...
When I set up a little scene, I save, then when something goes flaky, I exit, and run
Poser again. Sometimes it helps clear
Poser, as things can clutter up. You may have done this already.
My process, is to boot up.
Call up taskmanager (with the old 3 fingered solute).
I'll see then my max physical, my page file, and my total max (physical + virtual).
Load up a figure, or a prop, or a scene, and watch your page file value go up each time. Once it passes the physical value of RAM you have, things will slow down a tad. Note that if you load something, and then delete it, your page file usage will not go down to the value it was before you loaded the deleted item (in this case save the scene each time you are happy before loading the next item, then you can safely exit and rerun
Poser to clear the clutter should you be ready to render). Now when you press the render button, your page file use goes up some more, per light, and if you have shadows on, then more so, as you say. I note you have a fetish for the G2 figures at over 97k poly each, if only you had gone with P4 figures (self inflicted crisis, I say).
I'm running XP 32bit. The typical scenario of virtual memory is 3GB (HD space), in addition to physical RAM. Which is shared between the XP OS, and the user applications (half each).
I've set mine up to be greedy, and use more virtual memory, in addition my
Poser 6 has been set to know it can use more virtual memory, if it is present. Worth the effort to learn and do.
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I've found that to do well with any figure you really need to have a passion for that figure,
...and I hope you develop that passion for yours.