[netstuff]

дык, это ж просто:

left = 0;
right = 500;

onClipEvent(enterFrame){

if(Key.isDown(Key.LEFT)){
if(this._x < right) this._x=_x-1;
}

if(Key.isDown(Key.RIGHT)){
if(this._x > left) this._x=_x+1;
}
}