Both my new Dell (very fast and near silent) and the two ATI HDTV Wonder cards arrived this week. So after backing up the old system last night I tried to install Mythbuntu today.
The install itself went okay. I think most of the problems I had were self-inflicted. Unfortunately, my capture cards weren't automatically recognized, but I expected that because I had the digital-only VE version. However, even if I had the normal cards, I would have had to jump through hoops to get the cards recognized. But I think that's all okay now, the channel scan picks up the local stations and it's no longer complaining about no local channels.
Unfortunately, I haven't been able to establish connectivity otherwise. The web interface isn't active and the LiveCD front end doesn't want to connect either.