if (navigator.userAgent.indexOf("MSIE 6") > -1) 
    { 
        document.write('<link rel="stylesheet" type="text/css" media="screen" href="/Styles/ie6.css" />');
    }
    else if (navigator.userAgent.indexOf("MSIE 7") > -1) 
    { 
        document.write('<link rel="stylesheet" type="text/css" media="screen" href="/Styles/ie7.css" />');
    }
    else if (navigator.userAgent.indexOf("MSIE 5") > -1) 
    { 
        document.write('<script type="text/javascript" src="/Scripts/pngfix.js"></script>');
    }