To install Dantooine Enclave, you will have to extract Dantooine_Enclave.pk3 file from the .zip file into the GameData\Base folder of your Star Wars Jedi Knight: Jedi Academy game. The default path is:
"C:\Program Files\LucasArts\Star Wars Jedi Knight Jedi Academy\GameData\Base"
To uninstall Dantooine Enclave, you must remove Dantooine_Enclave.pk3 from the GameData\Base folder.