Help! falling Snow -please answer today

Hi!
I’m a high school student making a documentary using flash. I started using flash last year and still getting used to it.

Anyway… I saw the snow tutorial on this website and i plan on using it for 20 seconds (500 frames) in my introduction. It works perfectly fine, but after that time, it doesn’t stop. It keeps on going and going and going… plus it stays on top and

Can someone tell me how to make it stop or make it go into the background?

Thanks a lot.

I used the code provided by the tutorial. I know this is sudden by can someone answer today because i have to put it together before thursday. ;(