I did'nt implement USB support for my dock as I don't need it but i did make a "plugin" or a socket in the back for the ac-adapter. But i live in sweden so I bought a new plug and a new socket and just got some wire separated by the power switch so that power can be turned on and off as you don'nt always want to charge your player just cause it's in the dock! Anyways, I live in Sweden and I suppose you live in the US so this is what I would get:
http://www.radioshack.com/product.as...%5Fid=273-1641 along with the propper plug. As for the USB, there are some problems. You can probably find the propper plugs but when you start soldering all the leads for the USB plugs you'll get trouble. It's apparently very hard to get it right as USB is very sensitive on how well everything is connected. Some guy from germany who is trying to build the very same type of dock as you tried and the USB transfers ended up kinda bad. What you need to do is try to find the proper extension cable and NOT cut it!