I've been playing further with Mythbuntu. Using the Mythbuntu 9.10 installation (which uses MythTV 0.22), I never managed to get the Hauppauge remote working at all. And then it seemed to me that there was a rather a lot of hard disk activity while the computer really ought to have been idle.
A quick Google search suggested this might be solved by upgrading to MythTV 0.23. This was straightforward using links at the
Mythbuntu site. I also took the plunge and upgraded to the beta2 of Ubuntu while I was at it. This was straightforward, except I rendered the system unbootable by incorrectly answering a setup question relating to Grub2. Rescue was straightforward, and by running grub-install from a live Ubuntu CD, as described on this
useful guide to grub 2.
Somewhere along the line I was asked what remote I was using, and the upshot is that I now have a partially functional remote. It's not there yet, but there are a variety of handy wikis out there with sample configuration files for this model of remote, so I am confident I'll be able to set up full support for it.
So, now onward and upward for more complete testing.