Look at the Source Code of your html. Your swf div will have an id assigned to it. Add an html block and insert an internal style into it... a la:

<style type="text/css" media="all">
<!--

#swfcontent184 {
something like this code goes here
margin:0 auto or maybe text-align:center
it's late so i might be wrong, lol
}

-->
</style>

This is not really proper since it really belongs in the HEAD but it seems to work. You can also modify your external style sheet with some css or just add some into your header that is applied to all templates of that type. Such as the left_column template.

Good luck!