For the record, here is one way to get responsive behaviour with IE7 and IE8. As mentioned above the problem is that these older browsers don't support @media requests.
The solution is to use respond.js with older IE7 and IE8.
You can do this by downloading respond.js, installing it on your site and placing the following in the head of your page
<!--[if (lt IE 9) & (!IEMobile)]>
<script src="path-to/respond.js"></script>
<![endif]-->
or you can use Modernizr to test if the visitor's browser supports media queries and if it doesn't load respond.js . Downlod and save respond.js to your site as above, the place the following in the head of your page
<script>
Modernizr.load([
{
// test if browser supports medial queries
test : Modernizr.mq('only all'),
// If not, load the respond.js file
nope : 'path-to/respond.js'
}
]);
</script>
If you can't get either of the above methods to work for you, you can try using CSS3-mediaqueries.js instead of respond.js. They both work well.
Good luck ... it is an interesting time for web design!