I'm doing this quick tutorial because this little mod is required by so many other mods. I couldn't find any easy tutorials on the subject so I thought I would write one.
This mod was made by the original designer of the minecraft sound code and it allows custom music and sounds. For example you can put new music in C:\Users\[User Name]\AppData\Roaming\.minecraft\resources\mod\music
I strongly recommend that you make a backup of your entire minecraft folder which you can find in C:\Users\[User Name]\AppData\Roaming\.minecraft Simply copy and paste it into the Roaming (where .minecraft is) directory and windows will append a -copy to it. Now if something goes wrong you can delete your minecraft folder and remove the "-copy" from your backup and you're back in business.
|This kinda explains it all|
Open it with 7zip or WinRar
Go to C:\Users\[User Name]\AppData\Roaming\.minecraft\bin\minecraft.jar and open minecraft.jar with 7zip or WinRar.
Now drag and drop the files and folders from Audio Mod into minecraft.jar
Important: While minecraft.jar is still open delete the META-INF folder (if it's there).
There you are - done!
Please remember that modding anything implies risk and I am not making any promises that you will not encounter a problem. I'm simply explaining what worked for me. If you have difficulty try getting a new minecraft.jar, make sure you followed the instructions exactly, make sure you have the most up to date version of the mod and minecraft and remember that mods often don't work well together - which is why you backed up - right? - you did back everything up didn't you?