Best place to go is avsforum...
But here goes:
mpd-100 was the first generation card, no DVI output.
mdp-120 has DVI output through daughtercard, next generation tuner (better than 100)
mdp-130 has a QAM receiver, DVI output through daughtercard, best tuner--it will receive cable (QAM) signals if they are unencrypted, which should include all local HD
That's the quick and dirty...