Hi Colin,
Not sure how good it is or how easy it is to use as I have never had need to use it.... but you can translate language in Microsoft Office 2003 I would guess if you have the newer version then that will translate as well, I have a feeling it only does one word at a time though.
You will find a few on here http://www.google.com/search?q=language+translation&rls=com.microsoft:en-gb:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7SUNA I only looked at the first one http://www.freetranslation.com/ and all you do is choose the language i.e. English to Spanish and either type or cut and paste the text to be converted.