I had some troubles (re-)installing drivers under Windows Vista. I recieved an error either 'object cannot be registered' (or smthn like this) when i was trying to install drivers from setup, either 'not enough memory to run command' when i was trying to install drivers from Device manager. On some of the stages i also recieved: "A customized computer manufacturer driver is installed on your computer.". I am not sure what exactly was causing the problem, but i was able to install drivers only after i:
1. ran "sfc /scannow"
2. deleted MS DX 8.1 SDK (and several other programs, but i was able to install drivers just right after deleting dx 8 sdk; however, in your case it might be something else)
I also used some tool to "clean" registry, but i dont think it really helped.