I'm still researching this, but thought I'd post the problem, and what state i'm currently at in case someone has a quick bit of direction to give me.
I can't seem to get MythTV working, or my PVR-150 set up quite right. The PVR-150 has been detected, and added to the MediaDirector entry in the web admin automatically. I told the wizard not to config things for me as I don't have a supported provider. The instructions then told me to use the Computing>MythTVSetup. Well, clicking that causes the UI to flash slightly and then nothing happens.
I started following a post I found here that linked to a HOWTO on the mythtv site. In there there was a suggestion to run mplayer /dev/video0 to test things out. Doing that from the KUbuntu desktop I get a nice little mplayer window showing me the video feed from my satellite box into the PVR-150. Using the remote for my satellite box I can change channels, navigate the guide, etc. Okay, seems my connections are alright.
Next, the suggestion was to run mythtv-setup. Hmm, I get a message saying that mythtv-setup isn't installed but that I can install it using apt-get install mythtv-backend. Umm, why isn't mythtv-backend installed already?
I should point out that this is a sort of sandbox installation and I may well have done something previously that borked things. I might be best off with a fresh install.