I recently upgraded to Windows 8 preview, and had a very hard time installing the drivers for the SMS4 and NDS Backup Adapter Plus. I wasted half my day trying to sign the drivers myself yesterday...

Anyway, I continued to search, and you have to do this:
1. From the Metro or Desktop
2. Bring up Charms by mouseing over to the right of the screen
3. Go to Settings
4. More PC Settings
5. General
6. Advanced Startup > Restart Now
7. Trouble shoot
8. Advanced options
9. Windows startup options
10. Restart
11. Click on "Disable driver signature enforcement"
12. Reboot
13. Install the relevant driver, allowing the non signed driver to install
For the SMS4, just run the setup file I linked to here.
For the NDS Backup Adapter Plus, do just what you would do before, without using the Driver Signature Enforcement Overrider. No need to test sign the drivers or anything.

Source

These setting do not stick, unfortunately. If you restart your computer after doing this, you must repeat the above steps in order to use the SMS4 or NDS Backup Adapter Plus.