en el html...
colocas el code que llamas al flash entre las etiquetas <center> </center>
Código:
<center>
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=7,0,19,0" width="550" height="400">
<param name="movie" value="tu.swf" />
<param name="quality" value="high" />
<embed src="tu.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="550" height="400"></embed>
</object>
</center>