I've done this with a PVR350 tuner card and KnoppMyth. It worked well and had some nice features that the commercial DVRs don't have. You can do everything on it through the web including watching shows.
I really recommend the Hauppauge PVR cards, I used a PVR350 and a friend used a PVR500, both worked well.
Check out
http://www.knoppmythwiki.org/
er better link:
http://www.mysettopbox.tv/
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