>> Alternatively, could I boot up a live CD and copy configuration files 
>> from there?  I'm on the point of doing a complete reinstall, but I 
>> know this shouldn't be necessary.  Any help gratefully received...
>
> Do you find that sound works when using a live cd? that would be a 
> good sign of course.
> Copy files - if you retain the originals it cannot do any harm I would 
> think. I have done just that with display files such as xorg.conf.
Yes, sound with live cd works perfectly.  Is there an easy guide to
which config files I need?
>
> Have you done the ordinary thing of using the ubuntu forums? They are 
> not perfect, but are pretty good for many things.
> http://ubuntuforums.org/
I will have another go - no luck so far.
Cheers
Owain