I had a left aligned footer when I upgraded from 5.10 to 6, while keeping the look of 5. I fixed this by changing the parent DIV to "container" and it fixed everything, HOWEVER, this is not there in 6, so it will not work.
the way I ended up fixing all center justified tables in my template was by using a div wrapper.
basicly:
<div id='wrapper'>
<div id='footer'>
footer content
</div>
</div>
in the css the wrapper was center justified, and the footer was left justified. as a result, I have a centered table while its contents are laid out correctly