fai così:

codice:
<SCRIPT type="text/javascript" src="codebase.js"></SCRIPT>
<SCRIPT type="text/javascript">
width=screen.width
if (width <= "800"){
document.location.href= CodeBase + "Project_.htm";}
if (width >= "1024"){
document.location.href= CodeBase + "Project.htm";}
</SCRIPT>
ciao