Setting reg point?

I have this code for creating a border around images. (partly from the huge thread on resizeBorder here at Kirupa). The image is loading into a containerMC and that I can align top left, but this code I dont know how to align? Anyone?

//creating the border: 
this.createEmptyMovieClip('border', 3); 
with (_root.border) { 
   lineStyle(0.1, 0x999999); 
   _x = 100; 
   _y = 100; 
   moveTo(-100, -100); 
   lineTo(100, -100); 
   lineTo(100, 100); 
   lineTo(-100, 100); 
   lineTo(-100, -100);