If your
HDTV supports this, a cable card might be the cheapest way to go on some cable systems. Some systems might require you to have an
HD set top box to get all that you can get that you are entitled to. It's hard to tell unless you ask them. You might ask them then come back here before you make a final decision.
One thing is for sure, with cable, do not hook up the TV using a basic antenna wire (co-ax) from the set top box. You will either use component / with RCA stereo for sound or a digital sound connection
or HDMI takes care of everything (picture and surround sound)
or a
DVI connection (picture only, you need to add the sound using RCA or digital connections).