The problem itself is not a Poser 4 Specific problem, but is an inherent design flaw through Poser 6.  For example, Poser 6 has issues beyond 2GB of as well. I don't know about Poser 5 as I have never run it on a system with over 1GB, but I suspect the core code for all Poser versions is the same and has, simply, been added too and/or revamped over time to give us the newer versions. Hence, I believe that none of the versions after 4 was a total rewrite of the core code.

With that, here is a possible fix, albeit a risky one, but gives some insight into a solution otherwise not disussed here. Take note that this fix involves modifying the poser executable file itself (poser.exe).

http://www.keindesign.de/stefan/poser/3gb.html

Also take note that this addresses Virtual memory rather than physical