I assume that you have the body background centered using
body { background: #333333 url(imagefilename.jpg) top center no-repeat fixed; } or something like that.
Now create a div for the video code:-
CSS style:-
#videodiv { width: ??px; height: ??px; margin: auto; }
Markup:-
<div id="videodiv">
video object and nested embed tags here
</div>
and the div should center horizontally in any resolution like the background image.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.