It's pretty step-by-step in the readme file. You need 36 different sound clips in .wav format. After you've found the 36 .wav files you want, you need to change their filename to a seven-letter tag plus an ending number/letter. That lets the game know which sound to play when. The readme also tells which ending number/letter belongs to which clip. ("a" is a battle cry, etc.)
http://pirengle.icelus.net has a few soundsets I made. Like LennonCook said, it's easier to see it than explain it.