Leeneia,
Richard is right. The thing is, though, that the arranger's "right" in the arrangement *really* consists only in the newly contributed content, not to the previously existing material -- and yet your song book publishers and performance rights registrars will presume to claim control of the whole work and not just their added bit (chords, tweaked words...).
As in most things legal and contractual, everyone wants to interpret the wording to their own maximum advantage, and usually the guy with the biggest lawyer budget wins.
-Glenn