var browser, version, valid;

valid = false;

if (navigator.appName == "Microsoft Internet Explorer")
  browser = "IE";
else if (navigator.appName == "Netscape")
  browser = "NN";
else
  browser = "NA";

if (browser == "IE")
  {
    var temp;
    temp = navigator.appVersion.split("MSIE");
    version = parseFloat(temp[1]);

    if (version >= 5.0)
      {
        valid = true;
      }
  }

if (browser == "NN")
  {
    var indexValue, temp;
    indexValue = navigator.userAgent.indexOf("Netscape");
    temp = navigator.userAgent.substring(indexValue, navigator.userAgent.length).split("Netscape");
    version = parseFloat(temp[1]);
    if (version > 4.7)
      {
        valid = true;
      }
  }

if (valid == false)
  top.location.href = "invalidBrowser.html";