sudo apt-get install firmware-b43-installerand then rebooting. Sound worked straight straight away, without any additional configuration.
I have just installed Linux on my 17" Apple PowerBook G4. This page is an attempt to document what I needed to do to get everything installed properly. Firstly I downloaded Ubuntu Linux from the Ubuntu Linux PowerPC Downloads Page. After creating a CD using the Apple DiskUtility, I rebooted using the CD and pressing Cmd-Opt-Shift-Delete on startup. The Airport Express needs firmware in order to work. Luckily I had an old Netgear PCMCIA network card that I could use to connect to my wireless network while I downloaded the appropriate drivers. What worked for me was running the command: