You’ll need two files:
- hoc provisioning profile
- the ad hoc build (or .ipa file)
If you have a previous version of the app, it’s best to delete that from your device and iTunes before continuing.
Drag and drop both files into the Applications area of iTunes (see image) and sync. I haven’t seen the icon show up in iTunes using this method, but it does show up on the device (UPDATE: see Ad Hoc Build Icon in iTunes).
For subsequent builds, you won’t need the provisioning profile.