I ran across this info trying to install some development drivers for a device I own. The drivers were for windows vista 64 bit and I needed to install them on my windows 8 64 bit laptop. They've installed fine on my Windows 7 64 bit, but was prompted that the drivers were not digitally signed. However windows 7 just prompts you and asks if you want to install them anyway. Well for windows 8 that wasn't the case, the install just failed. Here are the steps I followed to get them to install....
So, one of the big issues I've had with the Windows 8 is that Microsoft forces you to use Digitally Signed Drivers (this isn't new, as Windows 7 requires them as well).
This is a problem for anyone who needs to install an unsigned driver to support their device. Fortunately, there is a workaround.
To get started:
From the Metro Start Screen, open Settings (move your mouse to the bottom-right-corner of the screen and wait for the pop-out bar to appear, then click the Gear icon).
Click "More PC Setting".
Scroll down, and click "Restart now" under "Advanced startup".
Wait a bit.
Click "Advanced Options"
Click "Windows Startup Settings"
When your computer restarts, select "Disable driver signature enforcement" from the list. After windows loads you can load your driver. You may need to right click your installer and select "Run as Administrator" when you run it. Reboot again once the driver is installed and all will be well.
Do remember that if your drivers are for 32 bit you need to have a 32 bit operating system to install them to, like wise for 64 bit will only install for a 64 bit operating system.