How to disable signed driver checking using BCDEdit in Windows Server 2008
An undocumented method of disabling the signed driver requirement for both 32-bit and 64-bit versions of Windows Server 2008 is to use the BCDEdit utility to make a change to the boot configuration. Because this feature isn't documented, Microsoft could remove it at any time. This procedure isn't something that a novice administrator should attempt to do, but it's doable.