I have installed Ubuntu Dapper on a Powerbook (G4 500mhz), and the sound is garbled. Listening to music with Rhythmbox is impossible. After searching Google, I tried using a .asoundrc file to play with the buffer settings, but the sound was still all over the place. I found another forum post stating that using OSS emulation would work, I tried this with amaroK, and while this combined with the .asoundrc file improves playback significantly, I still get enough gaps in the audio to make it a problem for music.
The card was detected as a "Power Mac screamer", although curiosly, it stopped showing up as my default soundcard under System->Preferences->Sound (which is now blank).
Here is my .asoundrc file: