I just upgraded by CPU, RAM, stuck in an SSD and installed Windows 7 RC 64bit (and Catalyst 9.6) and now my game is working fine (well I've only played for 30 seconds, I just wanted to check that I'd recovered my save games successfully).
You could try the Catalyst 9.6s but I doubt they're the solution.
Windows 7 has different UAC stuff so you could try turning off UAC to get past this point. Back on Vista 64bit I tried running the game as admin and in every compatiblity mode which made no difference, but maybe UAC is the problem.
Finally, you could try installing Vista 32bit or Windows 7 RC 64bit
.
I'm now more excited about finishing this series than playing whatever latest thing will stress my computer!
EDIT: If it's not a 64bit (specific to Vista) or UAC problem, then maybe it is something to do with going from dual core to quad core or hyperthreading or whatever (even though I had all that turned off).