Do you mean your mouse is broken or does only the AoD game not reckognize your right-clicking? If the former, just buy a new mouse ($5?), if the latter, try to get the latest drivers.
AFAIK, you cannot change the right mouse button. There is a file in AoD/config called "buttons.txt" where you can edit all other buttons but the mouse ones. It's just too strange to not have a working right mouse button...