Here are the tools you'll need:
1 tiny Philips head screwdriver (#0, I believe)
1 sharp blade or a flat-ended plastic spudger
1 tray for all your screws and bits
OPTIONALLY, 1 set of tweezers
Step 1: Disassembly
1. Put the two switches on the left side on "Hold" and "Voice" (flick them both UP).
2. Pop off the battery part, exposing the USB jack.
3. Remove the 3 screws on the back of the main unit.
4. Open the two halves with a knife blade or spudger, starting from the top (where the mics are) and working your way down both sides.
5. Remove the 4 mic guards so you won't lose them.
6. Remove the top panel.
7. Remove the Hold/Mode switch panel on the left side.
8. Pop of the back panel.
9. Remove the 2 mics from their cradles at the top and the gold contacts from their cradle at the bottom (next to the USB jack).
10. Carefully tilt up the main PCB against the long edge (let it hinge along the side with the Play/Stop buttons).
11. Unscrew the 2 Philips screws to remove the button assembly.
I stopped at this point, but you could probably also detach the Play/Stop buttons on the right and REALLY take the whole thing apart. It all depends on the nature of what you're trying to do.
Step 2: Reassembly
Once again, the detailed instructions are notes in the pictures, but here's the run-down of what you'll be doing:
1. Reassemble buttons and screw the whole assembly firmly into place. Watch out for the magnet in the speaker, which makes putting screws back in place a bit tricky.
2. Click down the main PCB so that the button assembly is reattached.
3. Nudge the mics at the top and gold contacts at the bottom back into their cradles.
4. Click the USB jack end of the front and back panels together.
5. Put the 4 plastic mic guards back into place.
6. Reattach the Hold/Mode switch assembly on the left side, making sure the switches are hooked properly into their respective tabs on the PCB.
7. Hold the top panel in place and carefully close the casing, working your way up towards the top from the USB jack end.
8. Screw the bottom panel back into place.
9. Reattach the battery compartment and make sure you haven't broken anything.
And that should be it, really!