function win_open(str)
{
  w_width= 800;
  w_height= 600;
  add_w = window.open(str,'ch','top='+(screen.height-w_height)/2+',left='+(screen.width-w_width)/2+',width='+w_width+',height='+w_height+',scrollbars=2,status=no,resizable=yes');
  add_w.focus(); if (add_w.opener == null) { add_w.opener = window; }
}