Although it might be heresy in today's world - in the past you would do the following non-css code. This works in everything up to and including today's browsers but - as I have said - it is heresy in today's world:
<center>
<table>
...
</table>
</center>
What you need is some way to tell that you want to center a table and the person is using an older browser. Then insert the "<center>" commands around the table. Otherwise - use css.
Surprisingly - if you want to center everything in the BODY area - you just can use the standard
text-align: center;
css command and in IE8 (at least) it will center everything on the page including tables.