If you have the problem in Ubuntu 10.04 LTS 64-bit that microphone’s not working with the Sound Recorder and Skype.
You can try installing the alsa backports which fixed the problem in Asus P7P55D with VIA VT1828S audio card.
Just run the command in Applications -> Accessories -> Terminal:
sudo apt-get install linux-backports-modules-alsa-lucid-generic
And finally reboot.