function popup(url,width,height) {
  screenwidth = (screen.width/2)-(width/2);
  screenheight = (screen.height/2)-(height/2);
  window.open(url,"Popup","width="+width+",height="+height+",left="+screenwidth+",top="+screenheight+",toolbar=no,status=no,resizable=no,menubar=no");
}