ASUS A8N-SLI Deluxe Socket 939 board:
There is an ACPI driver that gets installed with the Asus “AIBooster” utility and if you do not install AIBooster you will not get the ACPI driver and will end up with unknown device(s) in Device Manager even after installing all the other drivers. The solution is to install the ACPI driver, either by going into the correct AIBooster subfolder on the motherboard CD-ROM or using this driver.

Note that there are both 32-bit and 64-bit versions of this driver under different subfolders.