animating MCs on a sliding menu panel

[Super422]

I have a site with a sliding menu panel and I need MCs on that panel to animate (expand) when the MC appears in the center area of the stage and retract when the panel slides the MC out of the center.

Should I set up an if then for the values of the _x. coordinates of the MC, or perhaps instance another mc occupying the center 1/3 of the stage and do a MovieClip.hitTest function.

Does anyone have any thoughts or know of any source fla.s with something like this?

any help is good help
thanx