OK. Got it working!

All I did in the end was start MythTVSetup, delete all the Channel Config settings and then rescan the channels. I think before I'd probably done things in the wrong order, eg. ran MythFillDatabase before Scanning. I'm not sure that the screens I alluded to that were missing actually exist anymore?

Anyhow, it's now working and I can watch TV in MythTV with sound.

Next step is to work out what it actually does and see if I can get the Nebula supplied Remote Control working.

For those interested, I found the combination of these 3 guides most helpful plus the post on the www.dtvforum.info forum from DCallan on how to setup the Nebula card...

MythTVology - good step by step starting at how to set up FC3. I was brand new to Linux and was able to follow this from blank hd through to working FC3 setup.
www.wilsonet.com

Jani Talikka page (Australian) - Australian specific so also helped greatly - refers to DVICO card I think but still relevant.
http://www.users.on.net/~jani/dvico-mythtv.html

Martin Smith's guide - much more detail on how to make sure the DVB card is working.
http://www.ethics-gradient.net/myth/mythdvb1.html

Just remember, 'The journey is the reward!'.

Thanks

Nick