if (navigator.platform.indexOf('Mac') > -1) {
    //mac
    if (navigator.appName.indexOf('Microsoft') > -1) {
      //explorer
      document.write('<LINK HREF="css/m_ie.css" REL="styleSheet" TYPE="text/css">');
  
    } else {
      //netscape
      document.write('<LINK HREF="css/m_nn.css" REL="styleSheet" TYPE="text/css">');
  
    }
  } else {
    //windows or unix
    if (navigator.appName.indexOf('Microsoft') > -1) {
      //explorer
      document.write('<LINK HREF="css/w_ie.css" REL="styleSheet" TYPE="text/css">');
  
    } else {
      //netscape
      document.write('<LINK HREF="css/w_nn.css" REL="styleSheet" TYPE="text/css">');
  
    }
}