I've had this problem that I, for the longest time, never took the effort to deal with.
When my notebook boots up (a Fujitsu Lifebook S7010), Windows XP will activate the Add New Hardware wizard, but neither successfully adds the hardware automatically, nor offer any clue as to what the device might be, simple listing it as Unknown in the Wizard.
Today, I got around to allowing it to install without drivers, in order to look up further info. Lo and behold, when you view the unknown device's Properties in Device Manager, and in the Details tab, the Device Instance ID lists it as "ACPI/FUJ02B1/xxxxxxxxxx".
Googl'ing "FUJ02B1" took me to a Fujitsu Support and Download Page, which lists the device as an ACPI controller.
Downloaded the "acpi.exe" file, extracted the file contents (it's a self-extracting zip file), and used the Add New Hardware wizard to install the driver manually, and Viola!
Driver installed, Hibernation tab appears in Power Properties, and Windows no longer prompts to install a driver upon log-in.
Note added on 9 Sep 2009: This have apparently worked on a couple of other Fujitsu Lifebooks, including a C-6651.