if (/MSIE (\d+\.\d+);/.test(navigator.userAgent)){ //test for MSIE x.x;
 var ieversion=new Number(RegExp.$1) // capture x.x portion and store as a number
 if (ieversion<7)
    alert ("You are using an older version of Internet Explorer. This website works best with Internet Explorer 7 or higher.")
}
else