Ok, first off, I'm still quite wet behind the ears on this stuff. I have learned enough to set up a pretty solid HD projector setup in my apartment.

My question is this....

I am planning on signing up for Comcast's On Demand Platinum Digital package. This DOES NOT include HD programming. To get HD channels, you have to add on the Comcast HD package. Is this just a change made to the signal sent into my home through the coax or does it include a separate HD box?

I have a Samsung OTA HD tuner that (I believe) has QAM too. Could I just sign up for Comcast's digital package and connect the coax to my Samsung to get HD?

If Comcast provides a STB for channel tuning purposes, how is it different from my Samsung except that my Samsung can receive OTA signals?

Thanks for the help.

Comcast broadcasts their digital channels in QAM format which will contain unencrypted and encrypted channels. If your Samsung receiver supports QAM you should able to select the signal type from them menus and perform a channel scan. You will most likely receive your local HD channels through Comcast without a problem. Your mileage will vary with any other channels. If you subscribe to HD services, Comcast will provide an HD receiver to decrypt your subscribed channels as well as provide guide data. Guide data (for QAM channels) will not be available on the Samsung receiver.

Comcast does NOT have an HD only package.

HD locals are considered part of Limited basic (and IMHO this should be the case EVERYWHERE)

Non premium HD channels are considered either part of Digital starter or Digital Classic

The only "extra" fee is for the lease of the HD box ($5 extra for a standard HD box $4 extra for a DVR(plus $6 for DVR service)) -based on charges in Boston market Your charges may vary.

If your tuner supports QAM then you should be able to receive the unencrypted HD channels without any additional services. They just don't tell you this. If you currently have Comcast cable service try it.
However the unencrypted channels are most likely a subset of the digital channels that you currently can receive with your Samsung OTA tuner so you don't gain anything.