For Windows 8.1 do the following (The Windows 8.1 driver wont install otherwise):
1. 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).
2. Click ‘Change PC Settings’.
3. Scroll down, and click ‘update and recovery’
4. Click ‘recovery’
5. Click under advanced start up and restart now
6. Click ‘Troubleshoot’
7. Click ‘Startup Settings’
8. Click Restart
9. When Win8 restarts type the number next to \"Disable driver signature enforcement\" - I think it's number 7
When the computer restarts, go to Device Manager and right click on AirNav RadarBox. Update driver and point it to the unzipped 8.1 driver folder. Accept any warning messages and it will install and work.