I'd like to get rid of my leased Comcast cable box/DVR. Can I replace it with a purchased tuner/DVR, or is there proprietary or unique decoding content in those leased boxes?
Currently Basic channels are not encrypted, Premium are - but this is changing soon. All channels will be encryped "for your convinience" (don't get me started on this)
Ether way you go (TiVo box) or custom HTPC based solution, you'd still will need to lease CableCard from Comcast - thou it's typically a bit cheaper - $6-7/month
Supposedly there are some TiVo boxes on the ebay with lifetime TiVo service builtin, thou I don't know if its true, Normally TiVo service is an extra monthly charge
There also solution like this one
http://www.engadget.com/2011/08/18/hdhomerun-prime-cablecard-tuner-hands-on/ - but I don't know how good is it....
HTPC & Cablecard is possible (and very good solution), but it's extremely technical... If you want to cut the cord and have it easy and cheap way look for streaming boxes like Boxee Box and Roku