I already purchased an ATI TV Wonder 650 Card, and was wondering how to set it up to get my high numbered comcast channels without the set-top box, if it's possible.
If all you want is to record stuff from the major networks, over the air digit works really well in most areas. Also in most areas the digital signal from cable for the major networks is unscrambled. You would be able to record in HD from your cable with any card that advertises clear QAM reception.
Depends on your exact location. With cable you have reliablity but sometimes the signal is compressed. OTA you still have to worry about the antenna getting reception. Different channels can broadcast from different directions and there is even the chance that you are too close to the tower and lose reception from too strong of signal. But you get the best looking picture you can.
if you get good antenna reception (with digital, that means the signal doesnt cut out at different times of day or weather) then that will actually be superior to a cable's hdtv signal. ota is fully uncompressed, unfettered, untouched....