I don't believe you will be able to use the 4722 with the modulator - it works only with the 5000 series receivers.
Dish has a new HD6000 receiver out now that is an HD set-top-box, with an OTA tuner card due out this August. In order to receive HD from Dish, you will need to have a dish pointed at satellite location 61.5. Most other content comes from 119/110.
I bought a HD6000 new subscriber package, which included two dishes, receiver and switches for $399 from
www.dishdepot.com. Currently I receive both HBO and Showtime HD movies - both of which are now offering DD5.1 (HBO just started).
Bear in mind, though, HBO pan & scans their HDTV movies nearly to the point of rendering them unhealthy to watch!