function open_window_centered(url,name,newwidth,newheight,scrollbar)
{
      var pos_x = (screen.availWidth/2) - (newwidth/2);
      var pos_y = (screen.availHeight/2) - (newheight/2);
      cntwindow=window.open(url,name,'scrollbars='+scrollbar+',resize=yes,height='+newheight+',width='+newwidth+',left='+pos_x+',top='+pos_y);      
      cntwindow.focus();
}