if(navigator.userAgent.indexOf('Mac') != -1){
 document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="mac.css">')
}
if(navigator.userAgent.indexOf('Win') != -1){
  if(navigator.appName.charAt(0)=="M"){
   document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="win_msie.css">')
  } else {
   document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="win_nn.css">')
  }
}