Center flash in firefox nightmare

Hi guys,
What a friggin time i am having with this :help:
I have just discovered that the past few site i have built dont center properly in flash.
I thought that i had sorted this today using div with style sheet


<style type="text/css">
<!--
BODY {
 margin: 0px;
 padding: 0px;
 background-color: #000000;
}
#flashcontent {
position: absolute;
left: 50%; 
top: 50%;
margin-top: -265px;  /*minus half the height of the movie, so if your movie was 600 pixels high this would be -300px etc... */
margin-left: -382px; /* minus half the width of the movie */
}
#TopLayer {
position: absolute;
left: 50%; 
/*top: 30%;
margin-top: -265px;  minus half the height of the movie, so if your movie was 600 pixels high this would be -300px etc... */
margin-left: -382px; /* minus half the width of the movie */
background-image: url(barTop.jpg);
width: 765px;
height: 30%;
}
#BottomLayer {
position: absolute;
left: 50%; top: -65px;
margin-top: 500px; /* minus half the height of the movie, so if your movie was 600 pixels high this would be -300px etc... */
margin-left: -382px; /* minus half the width of the movie */
background-image: url(barBottom.jpg);
width: 765px;
height: 41%;
}
-->
</style>

I have discovered that if the user resizes the page then it all goes wonky :S
the top half of the movie dissappears :S

Example

Can some one please tell me how to fix this. html is not one of my strengths.
Thanks
Paul