no problem man, unfortunately if you want to go back to a jailbroken firmware I'm afraid you are going to lose all your music

, but thats nothing a 'quick' sync can't fix. But just boot into DFU mode (hold lock and home for 10 seconds, release lock and continue holding home untill itunes recognises the phone) and then restore the phone back to the custom 2.0 ipsw via itunes.