サイトで、コードを index.html または index.php に追加します。
その作業も joomla と wordpress です。
<!--[if IE 5]>
<script language="Javascript">
<!--
alert ("It looks like you aren't using Internet Explorer 7. To see our site correctly, please update.")
//-->
</script>
<![endif]-->
<!--[if IE 5.0]>
!--
alert ("It looks like you aren't using Internet Explorer 7. To see our site correctly, please update.")
//-->
</script>
<![endif]-->
<!--[if IE 5.5]>
!--
alert ("It looks like you aren't using Internet Explorer 7. To see our site correctly, please update.")
//-->
</script>
<![endif]-->
<!--[if IE 6]>
!--
alert ("It looks like you aren't using Internet Explorer 7. To see our site correctly, please update.")
//-->
</script>
<![endif]-->
<!--[if IE 7]>
!--
alert ("It looks like you aren't using Internet Explorer 7. To see our site correctly, please update.")
//-->
</script>
<![endif]-->
<!--[if IE 8]>
!--
alert ("It looks like you aren't using Internet Explorer 8. To see our site correctly, please update.")
//-->
</script>
<![endif]-->