If your harddrive is thrashing your basically out of luck. Whats worse, when it gets really bad, your render could be as low at 20% of cpu usage. If youve got some high polygon terrains, you can reduce them a little, save and restart the program. That will free up a little ram. Everytime i hit about 250-275megs ram used by bryce outa 320megs the thrashing gets bad and fast. Be careful about exiting bryce abruptly when its thrashing bad. Did that once and from what i can tell, it must have been accessing the huge object presets i had, corrupted the whole file and the original br5. Theres no substitute for more ram, had 512 on a file 1.15gigs in size and bryce took 4 days thrashing the whole time. Got a full gig and it did the same file in 17 hours.