var win; 
function poplisting(listing) {

	if (win && !win.closed) {
		win.close();
	}
	win = window.open(listing,"","scrollbars,width=600,height=500,left="+(screen.width - 600) / 2+",top="+(screen.height - 500) / 2);
	if (!win.opener) {
		win.opener = window;
	}
}