Are you looking to tether without a plan? I got this info from att direct but i have a plan:
Enable USB Tethering with the HTC Inspire 4G (PD98120)
Connect to the Internet on a Laptop Computer using the HTC Inspire 4G (PD98120)
* A qualified tethering rateplan:
o DataPro Personal with Tethering
o DataPro Enterprise with Tethering
* Download and install the HTC Sync software:
1. In your computer's web browser, open http://www.htc.com/us/support/inspire-att/downloads/.
2. Click Download - HTC Sync.
3. Follow on-screen prompts to complete download and installation.
Enable USB tethering
1. Connect your device to your PC via the included USB cable.
2. On your device, select USB tethering, and then tap Done.
NOTE: If your device does not prompt you, drag down the notification bar and tap the USB connection.
* If your account is not provisioned properly, a notification message will be displayed.
NOTE: For provisioning assistance, please contact customer care.
3. Access the internet on your PC.
Disable USB tethering
Unplug your device from your PC.