function getInternetExplorerVersion() {
    var rv = -1; // Return value assumes failure.
    if (navigator.appName == 'Microsoft Internet Explorer') {
        var ua = navigator.userAgent;
        var re = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
        if (re.exec(ua) != null)
            rv = parseFloat(RegExp.$1);
    }
    return rv;
}

function checkVersion() {
    var msg = "";
    var ver = getInternetExplorerVersion();
    if (ver > -1) {
        if (ver >= 7.0) {
            msg = "You're using a recent copy of Windows Internet Explorer. " + ver;
            document.write("<link rel='stylesheet' href='css/style_t.css' type='text/css'>");

        } else {
            msg = "You should upgrade your copy of Windows Internet Explorer. " + ver;
            document.write("<link rel='stylesheet' href='css/style.css' type='text/css'>");
        }
    } else {
        msg = "You're not using Windows Internet Explorer.";
        document.write("<link rel='stylesheet' href='css/style_t.css' type='text/css'>");
    }
    //alert(msg);
}

checkVersion();