//bounding as with _root.aa:
onclipevent(load){
//initialize it true
checked=true;
this._alpha=100;
}

//bounding as with the button:
onrelease(){
if (_root.aa.checked) {
_root.aa.checked=false;
_root.aa._alpha=100;
} else {
_root.aa.checked=true;
_root.aa._alpha=0;
}
}