the Apple brand ipod charger is outrageously expensive. i bought my 1st gen nano from a friend for $50, the Apple usb charger is $39.99. to make this unit, i will show you how to take apart a dc wall adapter without ruining it.
Step 1: Opening the Wall Wort
opening these can be quite difficult. i found that cutting of the cord at the base and prying the case apart is the easiest method.
I used a chisel to slice the cord at its base, no damage to the case.
As you can see in the photos the chisel is facing away from the plastic so it doesn't gouge it.
Step 2: Prying Apart the Wall Plug
in order to make the case able to put together again, the shells need to fit each other.
I used a flat head screw driver to pry the case open.
in the photos, i had to use a different plug, the wires leading to the primary coil were melted and not fixable.
Step 3: Desoldiering
next we need to desoldier the circuit board from transformer. this allows room for the regulator.
Step 4: Usb-ness
to cut out the hole in the case i used a dremel with the paper disk. this allows an opening for the usb plug. If you are trying to find the usb female plug, try exploring old mother boards, and usb hubs.
Step 5: Hot Glue
i used hot glue to attach the regulator to the inside of the housing. it was a tight fit. i also glued in the usb plug, try not to get glue inside the plug, if you do its ok. over time the glue inside the plug will wear away.
Step 6: Almost Done
now soldier in the AC to DC board. this converts the transformer output to usable DC current.
Step 7: Put'n It Together
now its time to trim up the long wires and glue the unit back together. the nippers below, i believe this is what there intended to do.