Hi, Welcome to Sitepoint
Add a doctype to your page and re-test.
Without a doctype all versions of IE go back to the dark ages and render much like IE5 and use the broken box model and forget to inherit font-size into tables (among many other things).
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
Avoid using presentational tags like Center and attributes like marginwidth="0" as they are depecated in strict documents in favour of CSS.