Hello,world! for RPG Maker XP

hello.rb

class Window_Hello < Window_Base 
  def initialize
    super(380 , 20, 220, 60)
    self.contents = Bitmap.new(width - 32, height - 32)
    @time = 0
  end

  def update
    if @time == 0
      self.contents.clear
      self.contents.draw_text(4, 0 , width - 40, 32, "Hello", 1)
    elsif @time == 100
      self.contents.clear
      self.contents.draw_text(4, 0 , width - 40, 32, "World!", 1)
    elsif @time == 200
      @time = -1
    end
    @time = @time + 1
  end
end

class Scene_Map
  alias old_main main
  def main 
    @hello = Window_Hello.new 
    old_main 
    @hello.dispose 
  end 

  alias old_update update 
  def update 
    @hello.update 
    old_update 
  end
end