use method G, because it is easy to apply and should cause no or very few problems
cat /proc/asound/card0/codec#* | grep Codec
Codec: SigmaTel STAC9205
Conexant ID 2c06
Method G: linux-backports-modules
does work: D630, D830, Vostro...
does work: Dell 1720
does not work: iMac
does not work: Dell Vostro 1400 (Earlier the headphones were working. After trying Method G the card itself was not recognized)
Description: You just need to install the package linux-backports-modules-generic (metapackage to keep it up-to-date when upgrading the kernel, that will install as a dependency the package linux-backports-modules-2.6.22-14.generic). Make sure you have activated the backport sources.[color=blue]［非常重要哦！！］
sudo aptitude install linux-backports-modules-generic
For Dell Latitude D630 also do the following (if you don't, the volume will increase with every sound played):
sudo gedit /etc/modprobe.d/alsa-base
In the editor, add the following line at the end of the file:
options snd-hda-intel model=dell-m42
Save the file and reboot to get sound working correctly.
If sound is too low, go to Volume Control's Preferences and add "Front" (and any other playback tracks) and make sure they are set to the maximum.
Problems solved :
speakers are muted and unmuted when headphones are plugged/unplugged
the internal micro works (not very well, but works)
Remaining problems with this method:
no known problems