Moving _x position w/easing?

I have a gallery with a menu that is a row of
thumbnails (horizontal–right to left). And a button
on each side of the tumbnail menu—and of course when
you click on the right button the menu scrolls to the
right and vise-versa for the left button. The code I
have on the buttons is pretty basic:

right_btn.onRelease = function(){
menu_01._x -= 20;

I’m trying to set-up the menu so that when you click on one on the buttons
the menu slides over so many pixels and eases out. And I also need the
buttons to know when the menu mc has reached its end(say the menu is only 400
pixels wide). I’ve tried a few different things with no luck.

Any idea’s or direction to a tutorial???

I would really any help.