got this ipod from the pawn shop and I want to sync music from my mac to this ipod with out losing the music that is already on it. when I do tried to sync my music from my mac to this ipod it told me that I was going to wipe out all existing songs and replace them with mine but I don't want to lose those songs that are already on there i just want to also have my songs from my mac on there with the ones that are already on there.