This is a new icon set made to kill the old lifeless bird that came with Adium. You could put those three icons: Adiumy_Online.icns, Adiumy_Offline.icns and Adiumy_Alert.icns into:

~/users/Library/Application Support/Adium/Custom Files/Dock Icons

Then launch Adium, sign on and open Preferences > Dock > Icon and select Adiumy Icon Set on the right of the window. Click 'Okay' and your Adium icon will be changed :)

If you want to change the "Away" icon, you can do this by open Adium's Content Package then go to Content/Resources and drag "overlay_away.tiff" into it. Click "Yes" to replace it.