Step 1: Parts
Vellema n 3w Amp : K8066
RadioShack 1/8" Panel Mount Jack: 274-249
RadioShack 4AA Holder: 270-383
RadioShack 9v Snap Connector: 270-324
RadioShack Minii Toggle: 275-624
RadioShack 12" Shielded stereo cable: 42-2497
Speaker from a set of computer speakers
Step 2: Build the Amp
Step 3: Cut the Bottom
Drill holes to mount the board
Drill two holes for the AA holder so you can secure it with a zip tie.
Step 4: Cut the Top
Step 5: Switches Etc...
So you might want to solder your power switches, led and stereo jack up now.
The case opens up so leave plenty of room to open and close it.
I used the resitor just soldered to the leg of the LED as shown here.