I have a basic subscription with a cable box. Have an HD TV. Picked up a DTA from the Comcast office. What does the DTA do? Will that give me HD on my TV?
Unless Comcast is encrypting local/basic (the FCC is authorizing them to do so), you should be able to plug the Comcast cable directly into your HDTV (as almost all of them have a "Clear QAM" tuner) and receive all those channels (most if not all local network stations in HD).
If Comcast is encrypting local/basic in your area, then I believe they should be providing you with a uDAT (AKA HD DTA), that you can hook-up to your TV via an HDMI cable.