Tutorial Serving Up Universal IE 6 Stylesheet
All good browsers plus IE 7 and up get REGULAR-STYLESHEET.css, browers IE 6 and below get a special stylesheet with stripped down basic-but-still-nice styling.
<!--[if !IE 6]><!-->
<link rel="stylesheet" type="text/css" media="screen, projection" href="REGULAR-STYLESHEET.css" />
<!--<![endif]-->
<!--[if gte IE 7]>
<link rel="stylesheet" type="text/css" media="screen, projection" href="REGULAR-STYLESHEET.css" />
<![endif]-->
<!--[if lte IE 6]>
<link rel="stylesheet" type="text/css" media="screen, projection" href="http://universal-ie6-css.googlecode.com/files/ie6.0.3.css" />
<![endif]-->