if (navigator.platform && (navigator.platform.indexOf('Mac')) > -1) {
  //mac users
  document.write('<LINK HREF="scripts/ibc-mac.css" REL="styleSheet" TYPE="text/css">');

  } else {
  //windows or unix
  if (navigator.appName.indexOf('Microsoft') > -1) {
  //explorer
  document.write('<LINK HREF="scripts/ibc-ie.css" REL="styleSheet" TYPE="text/css">');
      
  } else {
  //netscape
  document.write('<LINK HREF="scripts/ibc-ns.css" REL="styleSheet" TYPE="text/css">');
      
  }
  }