I had the powerdown problem in xp as well. I fixed it by changing from a usb to a ps/2 mouse (same mouse, different connector). That got me thinking that the problem might be a conflict between the usb 1.1 and 2.0 features. i disabled usb 2 in the bios and then shutdowns went smoothly, even with a usb mouse. since i don't have any usb 2 devices yet, this isn't a problem. hopefully there will be a bios fix in the near future