Yes, desktop. Onboard sound only.
Having realised that the method of wiggling the jack introduces a horrible buzz, I've given up on the rear panel - I think the sound on the motherboard is shot.
This is a dual-boot box with Windows. In XP I have got the front panel sound working nicely (oddly, by disabling the front panel jack detection in Realtek Audio Manager. A known problem). If I can just achieve the same thing in Ubuntu, that will do, but I can't find the equivalent settings..
Next thing will be to install a soundcard, but the box is a bit full so I would have to remove some other card. Not ideal.