Spontaneous reboots sound like a hardware or driver problem to me. I know that XP reboots automatically on driver failures. What operating system are you using? It could also be faulty RAM. Do you have any other memory-intense applications? Do you experience automatic reboots when using any other applications? It doesn't sound like it's Poser's fault, an application should not be able to reboot the computer, no matter what goes wrong. I suppose there's rather something wrong with the drivers or hardware, maybe an IRQ conflict or DMA problems. What you should try is turning off graphics acceleration and see if the problem still occurs.