Holding Down a Key: Execute ONCE

I'm very lost on my scripting for holding a button down and having the action take place once.

So thing is, I have code for pressing a button (which is the up arrow button)

This was suppose to show the animation for someone shooting constantly until released:

    if (Key.isDown(Key.UP)){
        fox.gotoAndPlay(16);
        deploy.gotoAndPlay(2);
        trace("Pressed.");
    }

Unfortunetly the results are:

Holding down the up key places out "Pressed." constantly instead of once.

fox.gotoAndPlay(16) stays on 16 rather progressing the animation (to which should come back to 16 at a repeated process)

deploy.gotoAndPlay(2) plays a sound but before: the sound played constanlty rather once) recently: sound never plays

I also need code that prevents the player from moving when holding down the up arrow key.

So in total, I want the player to be able to hold the up key, and everything executed is played once until pressed agan after release.

I heard about adding listeners:

     var myListener:Object = new Object();
myListener.onKeyDown = function() {
    KEY = Key.getCode();
    if (!this[KEY]) {
        trace("You pressed "+KEY);
    }
    this[KEY] = true;
};
myListener.onKeyUp = function() {
    KEY = Key.getCode();
    trace("You released a key."+KEY);
    this[KEY] = false;
};
Key.addListener(myListener);

but I can't understand this technobabble and everytime I try to work it, it only puts error outputs.

Please help. This needs to be finshed in under 4 days.