I made it work almost.
I have the video but no sound yet
Go in the computing tab and select software/mythtv, then browse all menus
I am in France so the default values are wrong since configured for the US. I used the DVD install since the CD install fails
http://forum.linuxmce.org/index.php?topic=1942.15My capture device is V4L:/dev/video0 Input Television
Then you need to create a video source, configure with the basics, no teletext... for me it's SECAM
Then in the last menu just choose the capture device and the video source and scan for channels : it works !
Next step is sound...
by default it's set to /dev/dsp, and the audio output of my PCTV is wired to the audio input of the sound board... still have to investigate.
If anyone has an idea in the meantime....