The best place to start learning iPhone/iPad programming in general is to read this book:
And more specific to your question, yes, apps are allowed to access the iPod music library in the phone, through the MPMediaQuery class and its brethren:
In general, I'm wary of Games Programming books. I find it better to learn from a normal programming book, and apply what you learn into games. Then you can use the Game Programming book as more of a reference.
I use this:
But I learned iOS from this:
You really need a good book, I recommend Beginning iPhone 3 Development by Apress.