Unable to tether Vista to a Mogul running 3.56.651.0

[wm8s]

My firm just upgraded my notebook to Vista Enterprise 32-bit (against my wishes!). My Mogul is running the most recent ROM, 3.56.651.0. Under XP, I had no problem tethering using the built-in WM "Internet Sharing" app over USB.

Under Vista, no joy.

I've tried a thousand things. I've downloaded the most recent version of WMDC. After disabling "Enable advanced network functionality" in Connections -> USB to PC, I was able to get WMDC to see the device, xfer files, sync, etc. But still no joy on tethering.

The steps I'm following (that worked on XP):
(1) on the device, I fire up Internet Sharing, select USB, and hit Connect; the phone connects to Sprint's Phone as Modem service (which I'm paying for) fine.
(2) I plug the device into notebook via USB cable
(3) the notebook complains "Windows needs to install driver for your Generic RNDIS" and offers "Locate and install driver software (recommended), "Ask me again later", or "Don't show...". I select "Locate and Install..."
(4) the notebook says it's installing the driver, but then complains:

=======
Windows found driver software for your device but encountered an error while attempting to install it.
Remote NDIS based Internet Sharing Device
A device attached to the system is not functioning.
=======

and then the driver install windows complains:

=======
Device driver software was not successfully installed
Please consult with your device ...
Generic RNDIS Failed
=======

Has anyone gotten _THIS COMBINATION_ (i.e., Vista on the computer, plus a Sprint Mogul running ROM 3.56.651.0) to work? I'm at my wits end.

Thanks!

...R