Unknown PCI Device

I get a message offering to install a PCI device when I reboot or refresh
Device Manager in Vista - yet no devices are shown to be Unknown.

The Unknown Devices program doesn't seem to work in my copy of Vista - all I
get is an empty screen although it says that it's detected 23 devices in the
status bar.

I've tried to locate the HKLM\Enum\pci key in the registry without success
(as suggested by a KB article for Win98).

Any ideas on how to identify this bugger? I'm using an MSI 975X PUE mobo
and suspect that it may be a game card built in - but haven't pulled the
specs to check it out.

Thanks for any help/suggestions!

- John