function isIE3()
{
    var vIE = navigator.appVersion.indexOf("MSIE ");
    return ((navigator.appName.indexOf("Microsoft Internet Explorer") >= 0) &&
            (parseInt(navigator.appVersion.substring(vIE + 5, vIE + 8)) == 3));
}

function isNN4()
{
    return ((navigator.appName.indexOf("Netscape") >= 0) &&
            (parseInt(navigator.appVersion.substring(0, 2)) == 4));    
}