I had what sounds like the same problem but it was way before SP1 and it happened at complete random. I had to tell it that i want to install the drivers manually, and point it to the system32 folder, and it would install. Tedious? Yes. Did it get the job done? Yes. As far as I know, they never released a fix. This was with Vista Ultimate 64-bit, and I've since gone to 32bit and didnt have the problem anymore.