Help with firing game sample

hey i tried using the scripts in the firing game sample located:
http://www.kirupa.com/developer/mx/fire.htm

in this game, you have to click to fire. but i need to fire using the keys. i already tried using

if (Key.isDown(Key.SPACE)) {

–instead of

on (release)

it fires but it doesn’t duplicate. please help me with the code.
tnx!!!