"Conditional comments only work in IE, and are thus excellently suited to give special instructions meant only for IE. They are supported from IE 5 up until IE9 (inclusive)."
I have had success with:
<!--[if !IE]> -->
<div id="start"><embed width="1000" height="300" src="/custom/files/Startbanner.html"></div>
<!-- <![endif]-->
<!--[if IE]>
<div id="start"><img src="/custom/img/startlanding.jpg" /></div>
<![endif]-->
where Startbanner.html contains GWD stuff that is shown only if "!IE" ie not IE5-IE9. If "IE" ie IE5-IE9 a static jpg is shown.