Music and other content is not part of a backup. It's copied as part of the sync process. But copying music or other content from your mate's iPhone is not legal unless you already legally own a copy of said content.
By the way, tagging a new question onto someone else's thread, particularly one that's over a year old, usually isn't the best strategy for getting assistance. It's better, and more polite to the person who started the thread, to ask a new question in a new thread.