[MX] Movie Clip "attraction"

How would I write a script making movie clips attracted to each other, while incoporating it into their own movement functions?
For example, “mc_1” has this script:
this.onEnterFrame = function () {
this._x += 5;
this._y += 5;
}
And “mc_2” isn’t loaded onto the stage until the viewer clicks, through a listener or just a plain _root.onMouseDown function.

A pre-made example of the movement I’m trying to get is the “Interactive Buddy” swf, found here:
http://www.flashplayer.com/games/interactivebuddy.html
The “Weak Gravity Vortex” under God Powers is exactly what I’m talking about.