ja genausowas hab' ich auch gefunden ->
"Microsoft Windows 98, Windows Me, Windows 2000 and Windows XP are ACPI capable. These operating systems do not support wake from S5 state, only from standby. However, in some ACPI capable computers, the BIOS may have a setting that allows you to wake from an S5 state anyway.
If there is no support for wake from S5 state in your BIOS settings, then you will be limited to wake from standby when utilizing these operating systems in ACPI computers. "
http://support.intel.com/support/net.../CS-008459.htm
das heißt aber, das es nicht unbedingt gehen muss, wenn das bios das nicht untersützt.