This applies to the Launchkey and Launchkey Mini [MK1]
Both the Launchkey and Launchkey Mini can have different instruments assigned to the Pads and Keys. When you are not in InControl Mode, the Keyboard will send its data on MIDI Channel 1, and the Pads will send data on MIDI Channel 10.
Simply create 2 different Software Instrument Tracks in your DAW and assign one to receive data from MIDI Channel 1 and the other from MIDI Channel 10 (depending on your software, this may be done in the DAW or in the Plugin itself).
Remember, the Pads on the Launchkey have fixed note data, but they are pre-mapped to control most Drum Plugins. If you are using Ableton, you can use the Drum Rack to customize the sound that each note triggers. Check out this video for details on how to do this.