This addon simply swaps out the default err_norage sounds for clips from the song "Out Of Rage" by Turnstile. Seeing as this is not an actual addon but rather a sound replacement, I don't think it will work with the curse client.
To install:
Simply extract the "Sound" folder into your WoW directory. Should look something like C:\Program Files (x86)\World of Warcraft.
This does NOT go into the interface folder, addons folder, data folder, anything like that. Just straight into the World of Warcraft folder.
If you only want to replace sounds for a certain race then only add that races folder into the Sound folder, delete all of the others.
(PCGilnean refers to Worgen race in Human form, PCWorgen refers to Worgen in Worgen form.)