Center a moving movie to stage

Im having a mental block, I have done this before, but I cant think how…

Im prototyping a quick flash golf game. I have a ball that bounces across the stage, fairly simple. I just need it so that the stage follows the ball’s ._x value, so the ball is always in the center of the stage regardless of its ._y value.

Simple I know, I just cant remember how to do it…