Let me get this right....
You want people to help you for free, to create an application which your friend will subsequently make money from????
Hmm, I think thats taking the open source community just a little too much for mugs!
Code it by yourself. You'll learn far more yourself as you have to tackle the various problems you'll encounter, BUT as its just you doing the coding, you'll end up with a commercially viable application which you could subsequently sell. Share the development with any number of others and you can't do that.
coding for fun is one thing, creating forums and community sites but coding for a commercial operation (your friends record store) SHOULD imply that your friend should be paying somebody to construct/develop a system for him. Alternatively, why not go grab a copy of oscommerce which really is open source and tailor it to your friends needs