ho risolto così:

Codice PHP:
<style type="text/css">

 body { 
     text-align: center;
    background-color: #717171; 
    <!--background-image:url(images/repeatingBackground.jpg);
        background-repeat:repeat-x;-->
 } 
#flashcontent { 
     position: absolute; 
     width: 900px; 
     height: 600px; 
     margin-left: -450px; 
     margin-top: -300px; 
     top: 50%; 
     left: 50%; 
     background-color: #000000; 
 } 

</style>
<script type="text/javascript" src="tools/swfobject.js"></script>
</head>
<body>

            <div id="flashcontent" >

            </div>

        <script type="text/javascript">
            // <![CDATA[
            
            swfobject.embedSWF("index.swf", "flashcontent", "900", "600", "9.0.0");
            
            // ]]>
        </script>


</body>