how do i make a character move when a key is pressed but not holding the key?

i am making a pac man recreation in flash, and i need to make the controls for pac-man, i want him to move forever when i press a key, but not holding it, so, can anyone give me the script for that? im using macromedia flash 8, and the actionscript version must be actionscript 2.0

I'm currently working on my own Pac-Man game. My problem at the moment is whenever my character hits an item, it lags LOL!

var PC01_ACCELX = 0;
var PC01_ACCELY = 0;

function onEnterFrame()
{

_root.PC01._y += _root.PC01_ACCELY;
_root.PC01._x += _root.PC01_ACCELX;

if( Key.isDown( Key.UP ))
{
_root.PC01_ACCELY = -1;
_root.PC01_ACCELX = 0;
}

else if( Key.isDown( Key.DOWN ))
{
_root.PC01_ACCELY = 1;
_root.PC01_ACCELX = 0;
}

else if( Key.isDown( Key.LEFT ))
{

_root.PC01_ACCELY = 0;
_root.PC01_ACCELX = -1;
}

else if( Key.isDown( Key.RIGHT ))
{
_root.PC01_ACCELY = 0;
_root.PC01_ACCELX = 1;
}
}