ATSC, QAM and NTSC are modulations used by the different providers to deliver a signal to your house. You cannot convert an NTSC modulation to QAM or ATSC, you need to purchase the appropriate tuner that can tune/capture the appropriate modulation.
ATSC modulation is used by local terrestrial broadcasts and you need an antenna to pick it up and you need to be within a certain range of the broadcast tower (usually less than 70 miles or so based on terrain). ATSC modulation carries a digital signal.
QAM modulation is used by cable companies (time warner, comcast etc..). It is used to carry a digital signal along a coax cable wire. You must subscribe to cable and have the cable directly connected to a QAM tuner card to receive the signal. The problem is most cable companies encrypt this signal thus forcing people to rent their set top boxes to be able to decrypt. The only channels that can be viewed with a QAM tuner card are channels not encrypted (also called ClearQAM).
NTSC modulation has been replaced by ATSC for terrestrial broadcasts here in the US. It is still used by some cable companies (along with QAM) to carry analog channels. It is also outputted by set top boxes via S-video, component, composite and RF.
Dish network uses none of the above. It uses another modulation called DVB (Digital Video Broadcasts). It is a digital signal but you must use their set top box for decryption. Once the signal has been decrypted by the set top box it is converted to NTSC for output through the component, s-video etc..
What you need is a NTSC capture card that will allow you to capture the NTSC signal coming out of your set top box. The irony is that you start out with a digital signal (DVB), it is then converted to NTSC (analog) and then you need to convert it back to digital by the use of a capture card to make use of it in the computer.