[switcher!]

самое простое:

package
{
	import flash.display.Sprite;
	import flash.events.MouseEvent;
 
	public class Example extends Sprite {
		function Example():void {
			graphics.lineStyle(2);
			stage.addEventListener(MouseEvent.MOUSE_DOWN, onDown);
			stage.addEventListener(MouseEvent.MOUSE_UP, onUP);
		}
 
		private function onDown(e:MouseEvent):void{
			graphics.moveTo(mouseX, mouseY);
			stage.addEventListener(MouseEvent.MOUSE_MOVE, onMove);
		}
 
		private function onUP(e:MouseEvent):void {
			stage.removeEventListener(MouseEvent.MOUSE_MOVE, onMove);
		}
 
		private function onMove(e:MouseEvent):void {
			graphics.lineTo(e.stageX, e.stageY);
		}
	}
}