I'm assuming this sound is for Goku, what you need to do is go to "C:\Program Files\Valve\Steam\SteamApps\email address\half-life\esf\sound\goku" folder.
Back up your old kamehame.wav sound, insert your new sound.
Things to know:
- Half-life uses 22050 HZ 16 bit mono, if you use anything else it will be converted everytime you create or join a game and you'll see the corresponding error.
- Open ended loops will crash the game in 22050 HZ.
Use 44 kHz or 11kHz, as i stated before HL will only play it as 22kHz so it converts it, i've had to do so for a couple sounds ingame now. For some reason it'll create some infinite loop if you have it at 22kHz originally. Oh yeah, 11kHz makes the .wavs sound like crap
Edit: One of the things Hars was suppost to fix.. like a year ago! Yeah Hars.. where's my fix?!