i checked out your site with IE, opera, firefox, netscape... I can't see your problem.. you might have activated a user specific CSS-template or some other option over riding the websites font-size..
I think you also should specify the fonts with CSS.. and dont use MS fonts ;-)
you also might want to specify alternative fonts if the user does not have yours installed (should almost never be the case..)
if you dont work with css too much, here an intro:
http://www.w3.org/MarkUp/Guide/Style