I am running Poser 7 on amd athlon 2.08 ghz processor with 512 mb of real memory and system managed virtual memory (80gb free disk)  I typically render three figures with clothing and props  but i use 800 x 600 or so sizes. (max 1024 x 768 cause I like to view the whole pic) I once did 3000 x 2000 for printing .

I sometimes reduce 4000 x 4000 textures down to 2000 or even 1000 depending on what they are used for . Background prop get lower res textures. These are named as file_med or file_low so there is no confusion over whats being used.

with a 32 bit operating system more than 4 gb of memory is wasted and you may find the system doesnt recognise the whole 4 gb but only 3.5.  If you run 64 bit then more memory is better because it 2gb +2gb per task for 32 bit apps, the system can put operating system tasks in extra memory.