Erm...
C:\Program Files\LucasArts\Star Wars JK II Jedi Outcast\GameData\base\textures
As you evidently don't know this, all of the game files are stored in the assets[number].pk3 files. .pk3's function like .zip's, and therefore have directories within them.
A suggestion: Use Pakscape to decompress the .pk3's into your base directory. That way you can look at/mess around with the original game files to see how stuff is done, without actually changing the game.
Subdirectories in the \base\textures folder are where textures are actually stored. If you want to use a texture in-game, put your textures in \base\textures\[yourmap] folder, then create a .pk3. Create a textures directory in the .pk3, and put the [yourmap] folder in that.
Unfortunately, richdiesal's site seems to have gone under.
Massassi still has a couple of good tutorials, though.
Good luck!