Can you post in Hardware support to get Dman_lfc attention as this is a hardware problem, Pinnacle has so many cards that if this is one of the oddball ones may have to be included/supported as cannot find EXACT match on supported cards.
Thanks for posting the link, but no problem has been solved in that thread either. Seems like Media Portal is ready to be uninstalled from my computer... a pity
There is no indication in tomarild's mediaportal.log that the same thing is happening to him.
Since MP requires more resources than the regular PVR application, try lowering the MPEG2 encoder quality and choose a lower resolution to start off with. You'll need to modify the encoder quality from within PVR application. Change the capture resolution via setup -> television -> capture cards -> select your card and click Edit
Also look at the CPU load while trying to watch TV, so you get an idea if your system is coping or not.