function check_browser()
{
  var version_number = navigator.appVersion.charAt(0);

  if (navigator.appName.indexOf("Netscape") != -1)
  {
    if (version_number < 3)
    {
      return false;
    }
    return true;
  }

  if (navigator.appName.indexOf("Explorer") != -1)
  {
    if (version_number < 4)
    {
      return false;
    }
    return true;
  }

  // unknown
  return false;
}


  if (check_browser()) 
{  
  <!--menu-->
  HEAD1 = new Image(50,20);
  HEAD2 = new Image(50,20);
  HEAD3 = new Image(50,20);
  HEAD4 = new Image(50,20);
  HEAD5 = new Image(50,20);
  HEAD6 = new Image(50,20);
  
  HEAD1on = new Image(50,20);
  HEAD2on = new Image(50,20);
  HEAD3on = new Image(50,20);
  HEAD4on = new Image(50,20);
  HEAD5on = new Image(50,20);
  HEAD6on = new Image(50,20);

  HEAD1.src = "img/nav/portfolio.gif";
  HEAD2.src = "img/nav/interfaces.gif";
  HEAD3.src = "img/nav/identity.gif";
  HEAD4.src = "img/nav/marketing.gif";
  HEAD5.src = "img/nav/aboutus.gif";
  HEAD6.src = "img/nav/contact.gif";

  HEAD1on.src = "img/nav/portfolioD.gif";
  HEAD2on.src = "img/nav/interfacesD.gif";
  HEAD3on.src = "img/nav/identityD.gif";
  HEAD4on.src = "img/nav/marketingD.gif";
  HEAD5on.src = "img/nav/aboutusD.gif";
  HEAD6on.src = "img/nav/contactD.gif";

  
  
}