Step 1: Required materials
One empty cereal box from a Kellogg's Cereal Variety Pack - I used Frosted Flakes, but you can choose your favorite cereal. It will not impact the outcome of this project. ;-)
Not required, but helpful: Soldering iron
Step 2: Remove speaker from card
Cut the speaker wire at the base of the circuit board first and then gently remove the speaker from the card. If you don't cut the speaker wire first you could end up ripping the wire from the base of the speaker and then you'd really need a soldering iron.
The speaker is fixed to the card with a small circular piece of double sided tape, so it shouldn't be too difficult to remove. Avoid the urge here to use your utility knife to "cut away" the speaker - you could accidentally cut right into the speaker itself.
Finally, strip about a quarter inch of insulation from the wires.
Side note: In case you're wondering, the Hallmark card is powered by a CR2032 3V Lithium Battery. This is the key ingredient for making an LED Throwie and is the power house for a bunch of other Instructables. The battery isn't necessary for this Instructable, but holding on to it could prove to be handy down the road. ;-)
Step 3: Prep headphones
Next, strip the wires. You may notice some fiber-like material interlaced with the leads themselves. Strip this stuff out with your utility knife or you will not be able to get a solid connection from your headphones to the speaker (thanks to Richard at my local Radio Shack on that one). Alternatively, you can use a soldering iron to burn this stuff away. I found this method much easier and a bit more effective.
Step 4: Connect
Once you've connected your leads (again, soldering here is a good idea, but not necessary) insulate and tidy up the exposed connections with some electrical tape.
Step 5: Prep cereal box
You'll also want to cut a small hole towards the bottom rear of the box to feed the headphone jack through. Feeding the wire through the back/bottom of the box not only makes it look nice, but also weights the box so that it doesn't fall forward on its face when you stand it up on end.
Step 6: Secure speaker, seal box and rock
Finally, glue back together the top and bottom of the box as it was originally sealed, connect an iPod and kick out the jams.