Cutting the hole for an IEC is tricky and tedious - Albert or others may have better methods than I, but below is what I've done. If your back panel is extremely heavy, the nibbler may not work and you'll need a "plan b".
- You need a cutter - I bought a nibbler from Radioshack. After removing the old cord, decide how to place the IEC and draw an outline of the hole. You'll need to make a template for this unless your IEC comes with one.
- If the IEC hole is positioned over the existing hole, begin nibbling from inside the hole, and work out to your line - but not past it. You'll need to drill a hole if it's not there.
- Finish off the hole edges with a file. A dremel moto-tool may work better than a hand file, but I do it by hand because the last thing you need is metal shavings on your circuit. It's very tedious, and you'll want to try for fit as you go. The IEC has about 1-2mm trim tab which doesn't leave much room for error.
- Once your IEC fits, and tightly is good - place it and drill the fastening holes (unless it's a snap in model), fasten it, and wire it up.
- When you're done - make sure you get ALL of the metal cuttings out of the unit that may have gotten away. I use an air compressor to air it out.