var browserAlertCookieName = "CookieAlerted";

function BrowserCheck() {

    var browerVersion = navigator.userAgent;

    if (navigator.appName == 'Microsoft Internet Explorer' && navigator.appVersion.indexOf("MSIE 6") > -1) {

        if (readCookie(browserAlertCookieName) == null || readCookie(browserAlertCookieName) == false) {

            alert('This website has been optimized for viewing in Internet Explorer 7 or 8, or FireFox 2 or 3. It may not display properly in the browser you are currently running, and some functionality may not be available to you.');
            createCookie(browserAlertCookieName, true, 1);

        }
    }
}

window.onload = BrowserCheck;