ubuntu-desktop , pulseaudio alsa sound in ubuntu precise

Hi,

I have noticed that when I installed ubuntu-desktop it is going to install some pulse audio packages and sound stopped working.
When I uninstalled ubuntu-desktop - sound started to works.

Could anybody please explain or navigate me to find out why is it happening ? Which "driver" is needed - pulse or alsa ?
Because I have read that ubuntu-desktop package is quite important but I need sound.

thank you for any clue/advice

Kind Regards,
Martin