The main sound problem on Ubuntu 9.10 is caused by Pulse Audio sound server. Simply, type this command in terminal to remove PulseAudio and fix sound with ALSA and ESound :

sudo killall pulseaudio

cp /etc/X11/Xsession.d/70pulseaudio ~/

sudo apt-get purge pulseaudio

sudo apt-get install -y esound esound-clients esound-common libesd-alsa0

sudo reboot

If previous solution did not fix the sound yet, here is another one. Type in terminal:

1. Removing all files in ~/pulse directory:

rm -rf ~/.pulse

2. Adding your user to audio group:

sudo adduser your_username audio

(ex: sudo adduser neothebest audio)

3. Removing pulse cookies

sudo rm ~/.pulse-cookie

I hope this things will be useful for you.