Mark or note the edges that need to be cut to open the AirPort Express case.

Use a dremel tool with a thin cutting bit to slowly cut around the marked edges. Cut evenly along the middle of the edges, and make several shallow passes to ensure that you don't accidentally cut into any of the components inside.

If you see sparks while cutting, it means you are cutting through the EMI shields. Reduce your cutting depth immediately to prevent further damage.

Be especially cautious when cutting next to the LED light, as the power wires are right next to the case wall. The wires are highlighted in orange in the third picture. Severing these wires may make the repair extremely difficult.