Show hide on (rollOver)

Hi, I am trying to accomplish this effect:

when I rollover the button number 1, the button number 2 disappears from the screen

when I rollOut of the button 1 butoon number 2 appears again…

I tried to write the code myslf but get errors…

this is the action I am trying to assign to the button number 1.

on(rollOver)=function(){
movieclipName._alpha=0;
}
on(rollOut)=function(){
movieclipName._alpha=100;
}