Trigger Ez Drummer in garageband with my digital drums

I have a SPD-S which I have connected to my Mac via MIDI / USB.

When I want to play in garage bands and use my SPD-S to trigger

drum sounds in GarageBand, I can not control what pads that will govern

and drum sounds.

How do you "Assign" drum sounds to different pads? I

can not find any settings in GarageBand where I can decide which

sounds played from the "what" Pad. I want to use my SPD-S

as a drum set.

For info, I use the following equipment:

- SPD-S

- Kick Trigger Roland KD7

- CME U2 Midi Interface

- IMac with Lion, and last Garagegand.

- Toontrack EZ Drummer