Helper help - inserting delimiters

My ruby skills are a bit underdeveloped, but I managed to whip up a Helper that inserts a delimiter at a fixed position in a number. Any wizards out there that can give tips on how to scale this to accepting calls for putting a delimiter at more than 1 position?

  def insert_delimiter_at(number, pos, delimiter="-")     begin       number = number.to_s       parts =       parts[0] =       parts[1] = number.from(pos)       number = parts.join delimiter     rescue       number     end   end