There is a hidden built-in Admin account in Windows 7 that has slightly elevated privileges when compared to a standard admin account that is set to have no password by default. Maybe try that when it gives you the two options. Also are you having any other issues with permissions on anything else besides the one driver?
You can activate this account by running your command prompt in administrator mode then typing:
net user administrator /active:yes
After that when you hit the login screen the hidden admin account will show up, you can try installing it then. After you are done I would deactivate it though.
net user administrator /active:no