Comment 2 for bug 232173

The comment above applies to both the EeePC 70x and EeePC 900 series (I can't speak for the EeePC 901 and EeePC 1000). They both do not have working microphones on a Ubuntu 8.04 install. However each has different sound hardware and a different fix.

EeePC 70x - Adding "options snd-hda-intel model=3stack-dig" to /etc/modprobe.d/alsa-base is a reported fix.

EeePC 900 - Adding "options snd-hda-intel model=auto" to /etc/modprobe.d/alsa-base is a reported partial fix to get the microphone hardware operating. However most people still cannot record reliably or with any volume. A full fix is not yet determined. The microphone done work under Xandros and XP.

Reference: forum and wiki