There's a hoop that needs to be jumped through to install unsigned drivers:http://windows.microsoft.com/en-US/windows-8/windows-startup-settings-including-safe-mode
It's working like a champ here. Actually, I'd modify those steps slightly:
1. Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings. (If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, click Settings, and then click Change PC settings.)
2. Under PC settings, tap or click General.
3. Under Advanced startup, tap or click Restart now.
4. On the Choose an option screen, tap or click Troubleshoot.
4a. On the Troubleshoot screen, tap or click Advanced options.
5. On the Advanced options screen, Tap or click Startup Settings.
6. Tap or click Restart.
7. On the Startup Settings screen, choose Disable driver signature enforcement.
8. Sign in to your PC with a user account that has administrator rights.