[sergwizard]

Можно так:

this.onMouseDown = function() {
	newBox.clear();
	startX = _xmouse;
	startY = _ymouse;
	dragging = true;
	
}
this.onMouseUp = function() {
	dragging = false;
}
this.onMouseMove = function() {
	if (dragging) {
    	    endX = _xmouse;
	        endY = _ymouse;
	        _root.createEmptyMovieClip("newBox",1);
	        with(_root.newBox) {
				lineStyle(.2,0x0000FF,10);
        		beginFill(0x0000FF, 5);
	        	moveTo(_root.startX,_root.startY);
	    	    lineTo(_root.endX,_root.startY);
		        lineTo(_root.endX,_root.endY);
		        lineTo(_root.startX,_root.endY);
		        lineTo(_root.startX,_root.startY);
		        endFill();
			}
		}
}