Here is a resource you should look at:http://www.hdtvtunerinfo.com/
Also, do some research on "clear QAM". Not every cable service provider is the same so you will need to research your particular provider. Most likely, you will need to invest in an "IR blaster" so your PC can control your cable box.
It isn't very easy or straight forward to get HD programing to an HTPC from a cable or satellite service. Almost every situation is unique.