I have Mac OS X Tiger. If you go to Preferences, you can select which of the two (or both) pre-installed dictionaries (actually one is a thesaurus) will be displayed when you look up a word. You can find the files for these dictionaries at Macintosh HD > Library > Dictionaries. The extension is .dict. Are there other .dict files I can dowload somewhere? I can't find any. I would like to add a French and Spanish dictionary, as well as the Webster English dictionary.