Can't get dimensions of EmptyMC

Ok, I’ve created an empty movieclip in _root and loaded an image into it but whenever I do trace(_root.newMC._width) I get a 0! I’ve had this problem in the past but never really looked into it!

Ah, while I’m at it, I have the following code:

with _root
  {
   createEmptyMovieClip("file", 0).loadMovie("someimg.jpg");
   ["file"]._x = (Stage.width - ["file"]._width) / 2;
   ["file"]._y = (Stage.height - ["file"]._height) / 2;
   lineStyle(3, 000000, 100);
   moveTo(0, 0);
   lineTo(800, 600);
   moveTo(0, 600);
   lineTo(800, 0);
  }

The problem I’m having with this is that when it looks for Stage.width it’s actually trying to find _root.Stage.width. How do I get around that without breaking out of the ‘with’?