Sorry - I didn't mention it, but I actually did run update-modules after making the changes.

I also ran alsa-autoconfig again, and had another play around with the sound options in Sound System.

I've done everything you've suggested except apt-get. Or rather, I tried it but it says there is no such package. I'm guessing that means it can't find it locally. Should I have a copy locally somewhere? I have no internet access though (can't get my wifi card working in Linux), so that's a bit of a problem :/

I'm going to boot off the CD and try again to find out what it does differently.