I maxed out 2 Gigs of RAM (2.8MHz CPU, 250G HDs) with the following in a scene:
Sydney
Hires Jessi
Hires Judy
SP3
two DM Mayan pillars
two extra large cloth planes
one IBL
four spotlights
CWShorty's Tamsen tex
AprilYSH's Jocosa tex
No stranded hair, no clothes, four sword props.

I started getting "You are running out of memory" messages. However, I added Miki without any problems. Haven't gotten past that step yet, but the "out of memory" messages have not appeared since I shut down P7 and restarted it the next day with my scene.