With the release of Ubuntu 6.10 (Edgy Eft), installing MythTV is now easier than ever. Enjoy the guide.
It is found here
Ubuntu is a great basis for a general purpose MythTV box and now comes with the latest version of MythTV (0.20) in its standard packages.
This guide focuses on DVB in the UK (Freeview), but much of it should be applicable to anybody installing Myth.