Turning a dropdown menu from AS2 to AS3

**Hi,

I would like to use this menu, but in Actionscript 3.

http://www.toxiclab.org/img/drop_down_menu.fla

When a user rolls over a button it goes to a frame labeled ‘over’ using this code which is on the button.

on (rollOver){
gotoAndStop(“open”);
}

In AS3 all scripts on objects are ignored. Hence this message:

WARNING: Actions on button or MovieClip instances are not supported in ActionScript 3.0. All scripts on object instances will be ignored.

Can anyone please help me code this or get it working in AS3, it is essential for a university project!

Thankyou Ben.**