This should help you get started.
<html>
<link href="manager.css" rel="stylesheet" type="text/css">
<script type="text/javascript">
if (screen.width < 1024)
link = document.getElementsByTagName( "link" )[ 0 ];
link.href = "manager800.css";
</script>
<head>
Thanks to: http://www.tek-tips.com/faqs.cfm?fid=4537
It basically changes the CSS file being loaded based on the users resolution.
Make sure all the different resolution CSS files are included with your skin package.
Not sure but you might have to use %skinpath% infront of your CSS filepath when making the change.