prova questo
codice:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
    "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html>
<head>
	<title>Flash - JavaScript resize example :: [ andr3a ]</title>
	<meta http-equiv="content-Type" content="text/html; charset=iso-8859-1" />
	<meta http-equiv="pragma" content="no-cache" />
	<meta http-equiv="Cache-Control" content="no-store, no-cache, must-revalidate" />
	<meta http-equiv="Cache-Control" content="post-check=0, pre-check=0" />
	<style type="text/css">
		html, body {
			padding: 0px;
			margin:auto;
                        width: 100%;
			height: 100%;
			background-color: #343434;//metti il colore tuo
			text-align: center;
		}
		#flashObject {
			position: relative;
			margin: auto;
			width: 650px;
			height: 180px;
		}
			</style>
</head>
<body>
<div id="flashObject">
<object type="application/x-shockwave-flash" data="opera_intro.swf" width="100%" height="100%">
<param name="movie" value="opera_intro.swf" />
</object>
</div>

</body>
</html>