the best way to do this is to use tables here is the code
You will have to play with the dimensions of the flash area to suit the size of your movie. But no matter what the movie will be in the middle this way.
Be sure to set your bottom, top, left and right margin to 0
<table width="100%" height="100%" border="0" cellpadding="0" cellspacing="0">
<tr>
<td height="50%" colspan="3"> </td>
</tr>
<tr>
<td width="50%" height="200"> </td>
<!-----####the transparent gif is just a place holder####--->
<td width="400" bgcolor="#CCCCCC">put your flash movie here<img src="transparent.gif" width="400" height="1"></td>
<td width="50%" height="200"> </td>
</tr>
<tr>
<td height="50%" colspan="3"> </td>
</tr>
</table>