The APC UPS I have with USB is simply seen as a USB battery by the OS. In the case of Windows XP, it integrates into the power control panel and simply acts similar to a laptop battery. You can set at what percentage you want a certain action to occur, and it happens when the UPS reports that it is at that level. I'd recommend turning on hibernate support, and setting the PC to hibernate at a certain percentage. That way even if you are away from the machine and had an unsaved document open, it would be saved by the hibernate process, along with whatever programs you had open at the time.