Here is free tool called ‘Driver Signature Enforcement Overrider’ that may helps you to install digitally unsigned drivers by creating your own unverified certificates. This tool supports both 32 and 64 bits of Windows Vista and 7.
Procedure for using this tool: Download and run the tool. Enable ‘Enable Test Mode’ and click ‘Next’ button and follow the instruction (restart your system). Now enable ‘Sign a System File’ and select the driver file that you want to install. Repeat it if you have more than one. That’s all.
If for some reason you are interested to revert it, launch the application again, choose “Disable Test Mode” from the main menu, and restart your system. The tool is free and clean and use at your own risk. [via-blogsdna]