Unsurprisingly, it looks like Sprint has disabled USB tethering.
I've installed the drivers, and the computer and phone successfully connect. Once USB tether is enabled, however, the phone will drop both 4G and 3G connections and throw up the following (see attached screenshot):
Error 67: Registration Failure. Your Sprint data service username and/or password may be incorrect. Please try again.
I know the software/ drivers are configured properly because I can pass the internet connection on to the computer when the phone is connected to the internet via Wi-Fi.
Really disappointed (but not surprised)...