http://www.macosxhints.com/article.php?story=20040426151111599 - Record and playback high definition TV signals
http://seth.mattinen.org/notes/hdrec.php -
I've just started this project, so these notes will be updated as I progress towards creating a working HDTV recorder out of an old Macintosh. I'll be using MacOS X for the operating system and FireWire (IEEE 1394) for the transport connection between the HD tuner and computer. A recent article on Slashdot presents other recording methods if you don't have a FireWire enabled tuner.
Apple FireWire news: soon, more AV/C support! - http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=269141
Macintosh FireWire Software - http://home.comcast.net/~macpvr/