Ti posto un vecchio esempio di Andr3a (www.3site.it)

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
	<title>SWF centrato verticalmente HTML 4.01 Transitional :: [ by andr3a ]</title>
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
	<META NAME="author" CONTENT="Andrea Giammarchi">
	<META NAME ="description" CONTENT="3site.it by andr3a">
	<META HTTP-EQUIV="keywords" CONTENT="Flash, FlashMX, FlashMX 2004, PHP, MySQL, SQLite, Tutorial, Tutorials, Script, Scripts, Class, Classes">
	<META NAME ="copyright" CONTENT="andr3a">
	<META NAME ="generator" CONTENT="ConTEXT V0.97.4">
	<META NAME ="robots" CONTENT="ALL">
	<SCRIPT TYPE="text/JavaScript" SRC="JS/flashMovies.js"></SCRIPT>
</head>
<body style="margin: 0px; padding: 0px;" onLoad="insert( 'Hswf', Hswf );">
	<table cellpadding="0" cellspacing="0" style="width: 100%; height: 100%;">
		<tr>
			<td id="Hswf">
				
			</td>
		</tr>
	</table>
</body>
</html>



dentro il file flashmovie.js

codice:
var Hswf = '<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://fpdownload.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=7,0,0,0" width="100%" height="260" id="zata" align="middle">';
Hswf += '<param name="allowScriptAccess" value="sameDomain" />';
Hswf += '<param name="movie" value="SWF/tuofile.swf" />';
Hswf += '<param name="quality" value="best" />';
Hswf += '<param name="scale" value="noscale" />';
Hswf += '<param name="salign" value="lt" />';
Hswf += '<param name="bgcolor" value="#ffffff" />';
Hswf += '<embed src="SWF/tuofile.swf" quality="best" scale="noscale" salign="lt" bgcolor="#ffffff" width="100%" height="260" name="zata" align="middle" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" />';
Hswf += '</object>';

function insert( id, swf ) {
	document.getElementById( id ).innerHTML = swf;
}
Questo è anche validato W3C e HTML 4.0 e funge sui vari browser

Ciao