Unfortunately, in order to view all the channels provided by the digital cable package you choose from your cable provider, you will need to rent an additional digital cable box and connect that to which ever TV tuner card you decide to purchase.
I subscribe to Comcast's digital cable service (I believe I subscribe to the "digital classic plus" package); however, I only have 1 digital cable box--only that TV has the ability to view all the channels. I have a "standard" cable box for a TV in my bedroom which allows me to get all the non-digital channels + Encore. For my PC, I use the Leadtek WinFast TV 2000 XP tuner card and have no box connected to it, and I only receive the standard basic cable channels on my PC. (no Encore and none of the additional "digital classic plus" channels).