I've been reading your post, and as far i can see, i really think that sysprep a folder then update the registry code to make hardware install thing "reads" another folder instead the default ;inf; only...
I read you did hang on to make by using that method to install any drivers but 'video'
I had the same problem too, but with WINDOWS 7. And it happens because there's and Standard VGA Driver that "bypass" and goes before the video drivers...
So... the point is, i had the same problem, i did have all the drivers, and all of them working but video.
So i just click in the devices managers the VGA Standard driver, and "update" it manually... choose the option that lets you install the driver manually, and it will prompt an Compatible Hardware List.
Just click the one who you own, should be only one in the list, if you mark the 'Show Compatible Drivers only' and then just let it install...
NOTE THAT I DONT KNOW IF THIS EVEN WORK, BUT I'M 'APPLYING' THE PROBLEM WHO I HAD WHEN DOING THE SAME THING WITH WINDOWS 7, THAT INSTALLED THE VGA STANDARD INSTEAD MY DRIVER
ITS JUST A THEORY, BUT IF YOU WISH, YOU CAN TEST IT. I'M DOING IT RIGHT NOW, AND IF IT WORKS, I'LL COME BACK WITH A NEW POST.
I apologize my bad english, my main its spanish.