When you are installing the ATI driver, I assume it is when you are running an HII action within Windows?
Are you calling a simple driver, or are you calling a package installation?
If you are calling a driver package installation, I would recommend checking the available command line switches to see if there is anything that can help elevate privileges.
You will want to look at the HIIHANDLER log. If it is in windows this should be in C:\LDProvisioning (Or is it C:\LDProvision?)
In addition, you can run HIICLIENT /previewall in Windows to see what it is detecting as the driver.