Game

I'm not sure that qualifies as a game. :-)

I think you need to look into the basics of AS, and ask some more specific questions. This is extremely simple, and seeing as you made a sample movie showing what you want to do you obviously have the ability to learn. Here's a start though:

make an animation MovieClip of a bar starting big and getting small, give it an instance name of "bar_mc" and put this on the _root timeline:
onEnterFrame = function(){
bar_mc.nextFrame();
}
keylistener = new Object();
keylistener.onKeyUp = function(){
if(Key.getCode()==Key.SPACE){
_root.bar_mc.gotoAndStop(Math.max(_root.bar_mc._currentframe-5,1));
}
}
Key.addListener(keylistener);