!!! NOTE: The August 14th, 2007 "Performance and Compatibility" update disables this.
Windows Vista x64 no longer allows you to disable the Signed-Driver requirement.
- Open an elevated command prompt (run as Administrator)
bcdedit /set loadoptions DDISABLE_INTEGRITY_CHECKS
(Note: the DD is not a typo.)
- Reboot the computer to be able to use unsigned drivers.