Hey Martijn,
Are you sure you meant frames? Or were you meaning to say tables? To center a movie horizontally, you can use Flash’s Publish settings and select Center for HTML alignment. To center vertically as well, create a 3 by 3 table with the widht and height 100%. In the center cell of your 3x3 table, place your animation. Your animation will be centered horizontally and vertically at all resolutions.