Page fade in - fade out - AS controlled

hey there!

Situation is as follows:

I have a Movieclip loading several other swfs via menu. Now if you are on page 1 and click on page 2 i want page 1 to fade out and page 2 to fade in. I thought about

btn2.onRelease = function(){
   while(container_mc._alpha>0) container_mc._alpha -= 10;
   while(container_mc._alpha<100) container_mc._alpha += 10;

Now the problem is i assume i need to put a speed variable somewhere in there to make it happen much slower…any ideas???

Thanks in advance