No funciona amigo
Te muestro como lo hice
(Dentro del HTML principal donde se aloja el movie flash) 
<head>   
Código Javascript
:
Ver original<script language="JavaScript">
function detectarflash(){
flashpage = "webinicial.html"
upgradepage = "webinicial.html"
nonflashpage = "html.htm"
cantdetectpage = "errorflashredirect.html"
 
noautoinstall = ""
if(navigator.appName == "Microsoft Internet Explorer" && 
(navigator.appVersion.indexOf("Mac") != -1 // 
navigator.appVersion.indexOf("3.1") != -1)){
noautoinstall = "true";
}
if (navigator.appName == "Microsoft Internet Explorer" &&
noautoinstall != "true"){
window.location=flashpage;
}
else if(navigator.plugins){
if(navigator.plugins["Shockwave Flash"]){
window.location=flashpage;
}
else if(navigator.plugins["Shockwave Flash 2.0"]){
window.location=upgradepage;
}
else{
window.location=nonflashpage;
}
}
else {
window.location=cantdetectpage;
}
}
</script>
  
</head> 
y
<body>   
</body> 
Gracias.!!!