Mouse over problem

I’m trying to make a button that it static until the mouse is over it, when the mouse gets over it a bar goes from the bottom to the top, and when the mouse leaves the button I want the action to reverse and make it go back to the bottom. I’m having a really dificult time doing this because mx doesnt like how I actionscript apparently… I havent read any tutorials on actionscript because it looks way too complicated for just what I need to do… please help?