Ok, XP and uncompressed video rules out a few things.
Most important, how big are the frames? and what is the frame rate?

How big is your Virtual Memory set for?
If you have more than one drive, is there plenty of space on each?

Try using the task manager to see how much memory Poser is using (you need to look at both the Mem Usage and VM Size columns) and how the amounts change as rendering progresses.