If it's really important that the translated text makes sense in the other
language, contact a human translator. Machine translation is almost
uniformly dismal, especially when idioms or special vocabularies are
involved.
That said, unless you want to upgrade to Word 2003 (which contains a link to
a web service) or buy dedicated translation software, your best automated
option is a web-based translation service such as http://babelfish.altavista.com. In each of those cases, availability depends
on which pair of languages you're using.