In a very short time, and easier than I expected, I managed to get sound working on my Acer Aspire 4320 running Ubuntu 7.10 (Gutsy Gibbon). Moreover, also getting the internal microphone to work, as well as an external microphone, didn't take much time either.
At the time of writing on the sound fix for my Aspire 4320, while I tried to copy several screenshots to a USB flash drive I had connected to my notebook I was greeted by a very unclear error message produced by the file browser Nautilus:
Error "Invalid parameters" while copying "/home/john...mixer).png".
When I looked a bit closer at the filenames of the files I wanted to copy it became clear what was causing the error...