function its() {
  var n = navigator;
  var ua = ' ' + n.userAgent.toLowerCase();
  var pl = n.platform.toLowerCase(); // not supported in NS3.0
  var an = n.appName.toLowerCase();
  this.mac = ua.indexOf('mac') > 0;
  return this;
}

var macstyle = '<link rel="stylesheet" href="includes/macfix.css" type="text/css" media="all" />';
var its = new its();
if(its.mac) {
	document.write(macstyle);
}