Once gentoo 2007.0 was installed, I had no sound setup yet.
My motherboard uses a 82801 intel chipset including an AC'97 sound controller.
I tried to compile the kernel 2.6.22 R9 to include Alsa (as proposed into the gentoo alsa help page :
http://www.gentoo.org/doc/en/alsa-guide.xml)
The sound level gnome applet would not allow me to unmute PCM nor change the amplitude. And I could not get any sound.
Then I found out that running
alsaconf in a shell would enable sound.
There was however a mixer setup error reported upon finishing the script:
'alsactl: set_control:1159: Cannot write control '2:0:0:PCM Playback Volume:0'
And Gnome sound began working.But PCM volume control was still unusable.
And I had to redo it upon every reboot.
I recompiled the kernel to remove all alsa and oss modules and only keep the basic sound support (reportedly named soundcore), not as a module but as a feature (that is selected as a * in menuconfig. not a M)
I then tried to install alsa-driver (as proposed into the gentoo alsa help page :
http://www.gentoo.org/doc/en/alsa-guide.xml)
And everything now works fine!