I have the same problem in XP Home and after reinstalls still does it. I opened the Admin tool Event Viewer and found the ACPI causing errors which is an error message I get too writing to a "protected memory" port that's not there. I tried changing all sorts of BIOS settings on my VT4X6 board and still Microsoft I think takes over the IRQ and puts them under one ACPI (power control) BIOS which is theirs perhaps? I tried going back to "standard" installation (which separates out the IRQs instead of in my case trying to put a number of devices on IRQ 5 or IRQ 11 depending on what I don't know, some service failure perhaps, three times it then decides?) which was even worse I thought. It has to do with the standby/hibernate new sager ATX power supplies which are quite brainy (and don't put high voltage at the power on/off switch as the AT specs did, kinda lousy for epileptics spilling a coffee over a word processing task) and by the way have had variable power tolerances between board and power supply. Maybe try a newer or different power supply? I went through a "new" one that was intolerant until I got a glow in the dark blue one from CompUSA (owned by a Mexican telephone company) just to get a boot. I have decided now to turn off all nVidia's helpful features that load at boot.
