In reference to the OPs original gripe, I too just recently started having my renders stall out (still running at 100% but going nowhere).  Again, copious use of props and interiors, monsterous skins (10+mb range) and IBLs with AO and depth of field.  I'm running Win7 64-bit with 8GB and although my reported memory usage never went above 70% I still have issue with scenes requiring more than average resources.  I was able to resolve the issue with a bit of trial and error however.

What works for me is to make sure the textures are loaded into memory before I try cranking out a HQ render.  I do a number of LQ test renders so that's usually not an added consideration.  The reason I say this is because I can almost guarantee a freeze up if I restart Poser and try to start a HQ render right off the bat.  When I do load up my HQ render settings I found that it's key to lower the max bucket size from 256 to 64.  That last bit seems to have been the real clincher for getting it to complete a render without freezing up (knock on wood). 

I actually found that the difference in render speed with varying max bucket sizes all fell within a range too small to be differentiated from a conservative margin of error.  We're talking less than +/- 30 seconds on a 20 minute render.  But this bit of verbosity is a bit tangential to the discussion at hand.  :)