Two weeks ago, I upgraded from 128MB to 384MB RAM, which has made all the difference for me. I would go higher, but that's all my ancient board will support. And since the upgrade, I haven't yet heard the hard drive crunching when doing a render. It was relatively cheap as an upgrade too ($30 per 128MB), so I'm very happy.

I'm guilty of being connected to the web while using Poser too. Usually, if I don't touch the computer during a render, nothing will crash. Merely clicking a button on the lower Windows toolbar during a render, however, has a high rate of causing Poser to freeze. I'm not sure the problem is necessarily an available memory problem, but Poser just seems to be too jealous of system resources to play with multi-tasking.