You can disable a driver verification using a command. Note that this might cause damage to your system's stability. There haven't been reported aggravated causes by OS corruption but you should stay informed.
Firstly, go to Start > Run and type bcdedit /set nointegritychecks ON. Reboot the PC, install the Vista driver with Administrator permissions, go to Start > Run and type bcdedit /set nointegritychecks OFF. Reboot the PC again and that's it. The webcam should work normally now.