You need a badder PC. That's why I went with a MyHD MDP-130 card. Not only do I get a OTA DVR, but I have a card that will play video files through a hardware decoder rather than a software decoder. True it only plays transport streams (mpeg2) or DVD file format, but converter software is available to convert the mpeg4 files to mpeg2 transport streams. Some of them take all night, but the studder is gone.
HD takes a lot of computer power and making sure you have nothing running in the background except what is absolutely necessary is crucial when you are using software decoders.