I found that high definition from DVICO Fusion DVB-T capture cards was really jerky after upgrading to 0.21 on a dual-core 4400 AMD. With 0.20, I hadn't had to do any tweaking to get hd going smoothly on this PC. At first I thought the problem might be the fact that I'd recreated the DVB cards to be able to record multiple channels from the same multiplex. I recreated the cards with only 1 recording per tuner allowed, but found that didn't help. I then found this post at http://www.gossamer-threads.com/lists/mythtv/users/323128 that talked about needing to change the playback profile from CPU+ to NORMAL. You can find the playback profiles as the third screen after selecting the option Setup/TV Settings/Playback from the frontend. So far things have looked good since I changed that.