Ejemplo de creacion de control personalizado para permitir contenido flash (SWF) en paginas ASPX 

<!-- REGISTRAMOS CONTROL --> 

<%@ Register Assembly="Flash" Namespace="Flash" TagPrefix="cc1" %> 

<!-- AGREGAMOS CONTROL A PAGINA --> 

<cc1:FlashControl ID="FlashControl1" runat="server"
        BackColor="#000"
        Quality="high"
        Movie="filename.swf"
        Height="180px"
        Width="389px"
        Align="middle" />

<!-- MUESTRA DEL RESULTADO FINAL EN CLIENTE (RENDERIZACION) -->

<object id="ctl00_ContentPlaceHolder1_FlashControl1" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://fpdownload.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=8,0,0,0" quality="high" movie="filename.swf" align="middle" style="background-color:#000000;height:180px;width:389px;">
    <param name="bgcolor" value="#000000"/>
    <param name="movie" value="images/940.swf"/>
    <param name="quality" value="high"/>
    <embed src="filename.swf" mce_src="filename.swf" quality="high" bgcolor="#000000" width="389px" height="180px" align="middle" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"</embed>

</object>