Help with FOR loop

Ok, guys, its me again. This is for the same menu bar slider thing ive been working on the past few days on and off. I have this for loop on a main button MC:

  
on (rollOver) {
 for (i=1; i<100; i++) {
  this._alpha = (100-i);
 }
}
on (rollOut) {
 this._alpha = 100;
}


Thats the code for the whole MC.
The movie can be viewed here. http://www.vitoxwebdesign.com/menu%20bar%20sliders.html
Now when the mouse is over, i just want the MC to fade to alpha 0, but it fades like instantanious. Is the loop working and just going really fast or what?
Thanks guys,
Mith