It’s pretty easy:
1. Do “Show Package Contents” on the SoundSet and/or DockIcon.
2. Replace the files in place with your own except for the Info.plist.
3. Edit the Info.plist with your own data in TextEdit or any other text editor.
4. Rename the SoundSet and/or DockIcon.
5. Open it to test it in Adium.
6. If it works, ZIP the SoundSet and/or DockIcon in the Finder.
7. Upload the SoundSet and/or DockIcon to AdiumXtras.com
Voilá! Note that 6 and 7 are optional, but recommended
