Poser 5 is believed to have some problems with using virtual memory -- transferring stuff between RAM and disk -- and certainly slows down a huge amount. I suspect that some of the lock-ups I have had may bave been illusory, and the program was chugging along in the background while nothing much appeared to happen. My own experience suggests that 1024MB will be noticeably better then 512MB, and that much RAM should be considered a practical minimum. 512MB works, but I know I keep hitting the limits.