update to last post.
For Mac, open HD Edit to create your tones or to open downloaded tones, open garageband and create a guitar track with pod hd connected. In garageband click on the guitar track you made to hear it live, and make sure its connected to the Pod HD. Now with both programs open you can hear the sound from garageband live through your computer as you change your tones in HD Edit.
If you dont know how to use Garage band, to create a track click Track > New Track > Click electric guitar >
and under where it says " my instrument is connected with" make sure you have these settings, Pod HD, Mono 2, System Setting, and check the box that says "I want to hear my instrument as I play and record". For PC use your music editing software to do the same.
Goodluck!