Ah, if you are talking about a map, then it should go to the \maps folder in your main \Dominions II folder. Sorry, I have answered to 'how to PBEM' -type questions so often lately I didn't realize this could be about something else...
The correct place for maps is the only place in your computer which has .map files, so if nothing else works try searching for those. '*.map' entered into the search field works.