Попробуй
<script language="JavaScript">
<!--
function checkPlugin(plgIn, theURL, altURL, autoGo) { //v4.0
var ok=false; document.returnValue = false;
with (navigator) if (appName.indexOf('Microsoft')==-1 || (plugins && plugins.length)) {
ok=(plugins && plugins[plgIn]);
} else if (appVersion.indexOf('3.1')==-1) { //not Netscape or Win3.1
if (plgIn.indexOf("Flash")!=-1 && window.flash!=null) ok=window.flash;
else if (plgIn.indexOf("Director")!=-1 && window.dir!=null) ok=window.dir;
else ok=autoGo; }
if (!ok) theURL=altURL; if (theURL) window.location=theURL;
}
//-->
</script>
</head>
<body bgcolor="#FFFFFF" text="#000000" onLoad="checkPlugin('Shockwave Flash','http://www.YOURSITE.com','http://www.macromedia.com',false);return document.returnValue">
</body>
<script name="Used by checkPlugin" language="javascript">
<!--
with (navigator) if (appName.indexOf('Microsoft')!=-1 && appVersion.indexOf('Mac')==-1) document.write(''+
'<scr'+'ipt language="VBScript">\nOn error resume next\n'+
'dir = IsObject(CreateObject("SWCtl.SWCtl.1"))\n'+
'flash = NOT IsNull(CreateObject("ShockwaveFlash.ShockwaveFlash"))\n</scr'+'ipt>');
//-->
</script>