Eliminating default language settings to all Office 2003 apps.
 

I opened Office default language to the Greek font in order to type a letter
to a relative. I then returned to the language site and restored English as
default and deleted the Greek.

However, Greek characters continue to appear as dates and punctuation in
Excel 2003 despite repeated attempts to re-establish English. Going to the
Language site, only English appears, but the Greek items will not revert to
English despite restarting numerous times.

There does not appear to be a default language setting specific for Excel -
only for Office, and changes there do not seem to work for the Excel items.