Best Way to Check Version of IE?

Just add this to the page...

<!--[if lt IE 9 ]>
<script>
var is_ie_lt9 = true;
</script>
<![endif]-->

Or in my case, I just wanted to display that they are using IE 8, then suggest to use a different browser...

<!--[if lte IE 8]>
    <h2 style="background-color:red;color:white;text-align:center;padding:10px;">You are using Internet Explorer 8 or older.  Please use Firefox or Chrome for proper display of this page.</h2>
<![endif]-->