im not giving a full blown tutorial.
but you do that by having the main buttons, and making
onRollover events, that trigger that highlight movieclip to follow
the mouse, and snap to the nearest buttons, and that movieclip has
that top menu attached, that will show up and ease in on the
Rollover. it will take you a while to make it. but yea thats how.
its all actionsctipt tweens.