Hm, I think you're out of luck on this one, but you can still try Snappy Driver Installer which might get the gpu drivers running.
It's 21gb large, DriverPack doesn't work on vista so you have to use SDI
Inform me if SDI installs the drivers correctly, run the windows experience index after installing the gpu drivers, then wait for it to finish the benchmarks. You should get Aero Glass and other Aero effects if it's 3+
EDIT: Yeah, might be the reason. Still, give it a try, might work although it might have to use an engineering sample