Unload .swf button and rollover sound button problems

Hi there…i got two problems actually…

one…how to use unload movie code in as 3? it is like this


When user click button on main.swf, pop up.swf will be load. then user click X button, i want to pop up.swf unload from main.swf…How?

One more…
When the mouse cursor roll over the button, one sound will play.after user leave the button area…how to stop the sound? because if the sound is too long, the sound seems to play till the sound duration finish…