function Is () {
    var agt=navigator.userAgent.toLowerCase();

    // BROWSER
    this.major = parseInt(navigator.appVersion);
    this.nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
                && (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
                && (agt.indexOf('webtv')==-1) && (agt.indexOf('hotjava')==-1));
    this.nav4 = (this.nav && (this.major == 4));
    this.nav4up = (this.nav && (this.major >= 4));
    this.nav6 = (this.nav && (this.major == 5));
    this.nav6up = (this.nav && (this.major >= 5));

    this.ie     = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));
    this.ie3    = (this.ie && (this.major < 4));
    this.ie4    = (this.ie && (this.major == 4) && (agt.indexOf("msie 5")==-1) );
    this.ie4up  = (this.ie  && (this.major >= 4));
    this.ie5    = (this.ie && (this.major == 4) && (agt.indexOf("msie 5.0")!=-1) );
    this.ie5_5  = (this.ie && (this.major == 4) && (agt.indexOf("msie 5.5") !=-1));
    this.ie5up  = (this.ie  && !this.ie3 && !this.ie4);
    this.ie5_5up =(this.ie && !this.ie3 && !this.ie4 && !this.ie5);

    // PLATFORM
    this.win   = ( (agt.indexOf("win")!=-1) || (agt.indexOf("16bit")!=-1) );
    this.mac    = (agt.indexOf("mac")!=-1);
    this.linux = (agt.indexOf("inux")!=-1);

}

var is = new Is();
if (is.ie && !is.ie3) theSheet="sizes_ie.css";
else if (is.win && is.nav4up) theSheet="sizes_nn_pc.css";
else if (is.mac && is.nav6up) theSheet="sizes_nn6_mac.css";
else if (is.mac && is.nav4up) theSheet="sizes_nn4_mac.css";
else if (is.win && is.ie3) theSheet="sizes_ie3_pc.css";
else if (is.linux && is.nav4up) theSheet="sizes_nn_lx.css";
else theSheet="sizes_ie.css"; // default for everyone else

var cssURL= '<LINK REL="stylesheet" TYPE="text/css" HREF="http://www.zdnet.co.uk/include/zduk/matrix/css/' + theSheet + '">';

document.write(cssURL);