function setDownImage(x){
    document.getElementById(x).src='images/tab_'+x+'_on.gif';
  }
  
  function setUpImage(x){
    document.getElementById(x).src='images/tab_'+x+'.gif';
  }  

  function hide_popup(x){
    document.getElementById(x).style.visibility='hidden';
  }

  function show_popup(x){
    document.getElementById(x).style.visibility='visible';
    setTimeout("hide_popup('yellow_baloon')",2000);
  }

  function show_sub_menu(){
    javascript:document.getElementById('sub_nav').style.visibility='visible';
  }
  
  function hide_sub_menu(){
    javascript:document.getElementById('sub_nav').style.visibility='hidden';
  }