how to pop-up window on center and top

[dgnzcn]

how to pop-up window on center and top with these codes please,
thanks


company.addEventListener(MouseEvent.CLICK , Popup_ac);

function Popup_ac(e:MouseEvent) {

var address:String = "company.php";

var jscommand:String = "window.open('" + address +

"','PopUpWindow','height=516,width=500,toolbar=no,s crollbars=no,resizable=no');";

var url:URLRequest = new URLRequest("javascript:" + jscommand + " void(0);");

navigateToURL(url,"_self");

}

contact.addEventListener(MouseEvent.CLICK , Popup_ac2);

function Popup_ac2(e:MouseEvent) {

var address:String = "contact.php";

var jscommand:String = "window.open('" + address +

"','PopUpWindow','height=522,width=473,toolbar=no,s crollbars=no,resizable=no');";

var url:URLRequest = new URLRequest("javascript:" + jscommand + " void(0);");

navigateToURL(url,"_self");

}