I'm actually amazed that you got P6 with only 512Mb of RAM to render out 4 figures and the Heroes Path scene at all, so for that WELL DONE.

I have run into problems with P7 giving me memory outages on large and complicated scenes with many Raytraced Reflections and the only way I got around it was to make my Adaption Threshold 2 and set my bucket size to 4 - not ideal and it took ages to render but it stopped all those annoying "Out Of Memory" messages.

To change your Adaption Threshold go to Edit>General Preferences and in the pop up box click on the Misc. tab.  Poser 6 seems to be defaulted to 0.01 so try upping that to around 1 and see how you go with it then.

Turn off texture filtering and drop your bucket size very low.  I tend to work in doubles so I will try at 32 and if that fails drop to 16 and then to 8 and then to 4 and maybe even to 2 if you have to push it.

To be honest any scenes that Poser has had issues rendering I tend to render as seperate pieces and then just layer them together in Paint Shop Pro rather than jump through hoops and mess with my standard render settings.  This is very easy to do and there is nothing to worry about so long asyou have your master pz3 with your scene laid out as you want it and you don't overwirite it (yes, yes, I have!)

Most of all GOOD LUCK!!!!!!!!!!