I am a novice Linux user but have learned a bit over the last week.
I ran through some of the stuff on the IVTV website and the https://help.ubuntu.com/community/Install_IVTV_Edgy website.
Now the cat /dev/video0 > file.mpeg worked fine and I was able to play back the file. So I started up LinuxMCE and then selected VIDEO from the menu. The MythTV gui started up and I actually saw a menu and everything (never made it this far before)....for about 5 seconds, then the screen went black again with just my mouse.