First off ALWAYS check the readme as most mods have some specifics that only apply to them.
Most mods of this kind come in a zip archive. if you open them up they usually contain a number of folders generally "base" and a folder with the name of the mod (eg "japlus"). If this is the case here is what you need to do:
- Right click the zip file and select extract (or extract using your favourite archiver (winrar, 7zip etc))
- When asked where to extract to choose your gamedata (not base!) folder (usually [plain]C:\Program Files\Lucas Arts\Jedi Academy\GameData[/plain])
and you are done. If this doesn't work have another look at the readme.
Using pk3s with mods
Each folder within "gamedata" represents a different mod. When you start up the game without any mods, the "base" folder will be loaded, along with any pk3s inside it. When you then change to another mod using the menu or start the game up with a mod, the contents of the mods folder (eg japlus or clanmod) will be loaded, along with any pk3s you have placed in that folder. Regardless of whatever mod you are running, JKA will always also load any pk3s from base.
Because there is a limit on the amount of stuff the game can load at once and because of conflicts, it is best to always install things you intend to use with just one mod into that mod's folder rather than base.