I was having the same problem with Win98, too, before I found Cacheman. Now I set up a scene & save it, then free up memory with Cacheman and render. This works for a while (12 or 15 renders), but the amount of memory that gets freed seems to get smaller & smaller, and eventually I freeze when trying to render again. At that point, shutting down & restarting the program doesn't help, I have to reboot the whole system. (I hope XP works better when I get it installed ....)