I'm stuck on a small problem with AS 2.0 and wonder if someone could help!

hi i’m trying to use the tweening things in flash i have sucessfully made a movieclip tween in and now within that movieclip is a button that sends you further down the timeline
what I’m trying to acheive now is to get the mc to tween back out then go to the specific frame so just using the flash 8 help files i’ve sort of worked out that I think i need to place this in the first frame of the moviclip that contains this button :

var tween_handler:Object = new Tween(_root.firstmenu, "_x", Bounce.easeOut, 176, -176, 25, false)
content2_btn.onRelease = function ():Void {
//I think something should go here but I'm not sure what... this is whats bugging me :-(
 tween_handler.onMotionFinished = function() {
  _root.gotoAndStop(5);
}
}

thanks for any help u could give!