An updated (Sassified) version of Andy Clarke's Universal IE6 stylesheet for IE7 and down.
To hide all your other stylesheets from Internet Explorer 7, wrap them inside this Conditional Comment.
<!--[if ! lte IE 7]><!-->
/* Stylesheets for browsers other than Internet Explorer 7 */
<!--<![endif]-->
Then add the Universal Internet Explorer 6 stylesheet.
<!--[if lte IE 7]>
<link rel="stylesheet" href="css/universal-IE7.css" media="screen, projection">
<![endif]-->
This is how I'll be 'supporting' IE7 and IE6 unless a client requires different. I've coded the Sass to suit my way of working but hopefully it makes sense. Fork it and pull it apart.