Seems that building my own PVR box isn't really going to work out for HD since I forgot about the up and coming Digital Rights Management schemes that are going to be all over the place.
For the home brewer, this means their solution won't work if they upgrade to high-definition cable, because the cable box won't send a readable signal to any tuner card that isn't part of a locked-down environment, such as TiVo or Windows Media Center.
You could always unplug your cable box and record free HDTV off the public airwaves, but perhaps not for long. The industry is trying to get Congress to make it illegal to build TV tuners that record broadcast HDTV without including DRM on the recording.
from wired news.