How Do I make Sounds Stop (fade out)!!

How Do I make Soundss Stop!!

I am currently in the midst of making a soundboard. But it's a little more complicated then a regular one. I have made the soundboard and it works fine..

However I want the soundboard to function so that...Let's say I click "Button 1" which is a 30 second clip.....

at any time during that 30 seconds of play I want to be able to click "Button 2" and in doing so I NEED "Button 1" to stop playing the sound or even better to fadeout quickly.

Right now i have it so that button 1 and 2 simply overlap each other when you click both as seen here

http://www.swfcabin.com/open/1310086712

Any help would be so awesome..Especially if you could tell me how to fade the sounds!