Go to Control Panel -> Display Properties -> Appearance Tab and click Advanced. Check each entry to see if any of the font sizes are larger than normal or if stuff is bolded that shouldn't be.
However, ar you sure it's not just ClearType (the worst invention ever IMO lol)? In IE7 you can turn this off by going to Tools -> Internet Options and then going to the Advanced Tab. Untick "Always use ClearType for HTML" in the Mulitmedia section. Not sure about Firefox or Outlook though, sorry.