I think I found your problem. If your looking at the Driver version through the Device manager then it says Version 8.512.0.0 am I not right?
Go into CCC (Advance) and go to Information Center, then to Graphics Software. If you look, it should say:
Driver "PACKAGING" Version - 8.512.xxxxxxx
Catalyst Version - 8.7 or 8.8
If I am reading this right, then I believe that Vista is reading the driver version as the packaging version and not the catalyst version.
BTW, When the hell did Catayst 8.8 come out?
There coming out too fast. T_T