function popup(width, height, url)
{
	var cx = width, cy = height;
	var left = (screen.availWidth - cx) / 2, top = (screen.availHeight - cy) / 2;
	var params = "left=" + left + ",top=" + top + ",width=" + cx + ",height=" + cy + ",resizable=1";
	var wnd = window.open(url, 'selection', params);
	wnd.focus();
}