Re: VDPAU 9400GT MPEG2 artifacts
I feel your pain. I've given up on vdpau on myth for the moment. At least for mpeg2 files. I'm running mplayer with vdpau as video player under myth, but my playback profile for livetv etc. is not using vdpau.
I tried different drivers, did a fresh test install, tried release and testing repos, still get random blocks.
Interestingly enough I installed xbmc the other day and I think playback of mpeg2 files with vdpau was fine there, but will need to double check confirm that it was really using vdpau.
If playback is fine there it would be interesting to know why and what is different (questions I can't answer with my limited knowdledge).