Drawing Bord Questions

Hi,

There is a Tutorial for making a Drawing Bord in the site…
(http://www.kirupa.com/developer/actionscript/drawingboard.htm)


_root.createEmptyMovieClip("line",1);
 
_root.onMouseDown = function(){
 line.moveTo(_xmouse,_ymouse);
 line.lineStyle(2,0x000000,100);
 this.onMouseMove = function(){
  line.lineTo(_xmouse,_ymouse);
  updateAfterEvent();
 }
}
_root.onMouseUp = function(){
 this.onMouseMove = null;
}

How can i Limit the area where it draws ?
and, I placed the code in the first Frame (it’s a Single KeyFrame) but it still draws in all of the frames of the movie…How can i make it Stop drawing on a mouse Press?

Thank You,

Elements