function popupCenter ( url , width , height , param) {
		var top = ( screen.height - height ) / 2;
		var left = ( screen.width - width ) / 2;
		if ( param ) {
			url = url + "?urlTo=" + param;
		}
		window.open ( url, "", "top="+top+",left="+left+",width="+width+",height="+height + ", fullscreen=no, toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=yes, resizable=0");
	}