Ok, this is somewhat interesting and I'm wondering why Apple with their MPEG QuickTime options haven't arleady done it - especially since regular tvs have only 640x480 res - you can get a lot of mileage on a 120 Gig disk. But I wonder if you'd be able to switch channels with the software or have to do it manually. The interface they talk about has buttons on the tower, not what I would want. Go all software, including the cable box interface and you could have a very cool system - add an extra monitor and you'd have the perfect setup.
http://www.cnn.com/2002/TECH/ptech/11/29/sproject.hs02.media.center/index.html
http://www.cnn.com/2002/TECH/ptech/11/29/sproject.hs02.media.center/index.html