I'm using WIN98SE on a P3 w/384meg ram
I'm able to render scenes with up to 3 or 4 figures depending on their clothing and other props loaded; after that...forget it.

1st: make sure you turn Everything else OFF, including virus progs and any 'cutesie background apps'

2nd: A work around is to render multiple 'partial' scenes and then bring it all together in Photoshop, Paintshop, whatever.

I've tried some of those Rambooster apps but never saw any help with Poser but I think I saw some improvements when working with Bryce...?