You can use rivatuner 2.1 or ntune, and I believe you can set it to save the OC on reboot, not 100% sure though. Right click and then "run as administrator," or you can disable driver signing alogether:
However, the solutions presented by Kaspersky to disable Mandatory Kernel Mode and Driver Signing fail to deliver streamlined usage. And there is a simpler war. All you have to do is type "cmd" in the Search Box included in the Vista Start menu. Next, press Ctrl + Shift + Enter to open a command prompt window with elevated privileges. Now enter bcdedit /set loadoptions DDISABLE_INTEGRITY_CHECKS in order to disable Driver Signing and reboot.