2GB of RAM is part of your problem too I reckon. For multi-figure renders you really need more. I used to be limited to 2 Vicky 4s in a scene. Upgrading my RAM to 4GB and using the /3GB switch allows me to do a lot more. Since the upgrade I've already managed one scene with 5 fully clothed Vicky 4s and I reckon I might manage to squeeze a bit more in.
Thats in Poser 7 running on WinXP SP2.
If a complete PC upgrade is out of the question a RAM upgrade would be a good investment if you want to do multi-figure scenes.

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