Replacing sounds

I have played the unreal games forever, but never really got into the whole mod thing. I mean I have downloaded new skins and maps, and have played mods, but never really looked into the technical side of modifying the game.

Which brings me to my question. How do you add customs sounds, and more to the point, does anyone know of any? (I want to find a good sound to replace the Assault rifle default one). I know in Counter Strike that they are simple sound files for each sound that are easily replaced, but how about Uneal, specifically UT2k4?

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