I'm running Poser 5 on a PIII 550 with 640MB of RAM. It has only crapped out once, after running for over 24 hours, but I have only used the Material and Pose rooms. I've just tried the FireFly renderer. I'm seeing how the Mil characters and their stuff work with the new renderer -- it is the most important new feature for me. I'll try adding some hair and dynamic cloth this weekend to see if I have any problems.