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Most HDTVs have a QAM compliant tuner. You have to check the manual to be sure. If you bought an HDTV from say Walmart and got the very basic cheap model, it may not have a QAM tuner. It may not have any tuner at all (they would call it an HD Monitor then)! QAM is the method all cable companies use to compress HD. (Something like what JPEG is to images for your computer.) That compression is different than what the satellite companies use to compress their signals. So a QAM tuner does nothing for satellite signals.

QAM is NOT scrambling, however. Scrambling is a method of secure transmission where you need a "key" at the receiving end to "unlock" the program. That requires a set-top box. The cable companies are allowed to scramble any channel EXCEPT what is broadcast in your local area.

For $6/month you will receive all the 4 Network HD feeds, plus DiscoveryHD*, plus a few others in HD. It's the "few others" (like A&E-HD, FX-HD, ESPN-HD) that are costing extra to unscramble with a box because the Network and Discovery* HD feeds are already free and don't need to be unscrambled. They come through just compressed (QAM).

*For a while Comcast had The Weather Channel-HD for free, now it's Discovery-HD for free. Next year it might be Food Channel-HD for free. They seem to like to tease us. But you'll always get the major networks in HD for no extra cost.

If you have an HD television, open the manual to the "Specifications Page" and in the area where it specifies the tuner(s) look for the abbreviation "QAM" where it lists "Digital Cable".

Now decide if getting A&E, FX and ESPN etc. (you already get these in analog, remember) in the higher resolution is worth the extra $6/month.

"On-Demand" programming is a whole 'nother ball game. That DOES REQUIRE a SPECIAL set-top-box (that can communicate in both directions).

Hope this helps.

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