You can turn off driver
signature enforcement temporarily using the advanced boot options (F8). However, that'd need to be done at every boot.
I wonder where those "protected files" originated. There are apparently several levels of signing. Beta drivers
(I frequently test beta graphics drivers) require you to click a permission button when you install them. I've also been able to install graphics drivers with modified .inf files.
Windows 7 X64 is supposed to be more finicky about unsigned drivers than the 32 bit version. You can't install them at all if driver signing enforcement is on.