There are several clarifications that likely need to be made here before you get to far ahead of yourself.
1. Your projectors DISPLAYS HD content, or your projector IS a HD projector? The two are not the same. Just because I can understand Spanish when someone speaks it, is not the same as me being able to fluently speak Spanish.
2. When outputting from a computer to a projector, you must very carefully setup your PC to best match the projector. This is a lot more complex then just hooking up the VGA cable. You need to set your resolution and refresh to match perfectly, or else you may not get optimal results.
3. Downloaded HD is not going to be the same quality, most likely, as what HD DVD or Blu-ray will deliver. Though it can be very good. Since it isn't the same, it just is going to be more of a representation of the quality you can get rather than the final result.
4. HD delivery from OTA receivers, cable, satellite, Blu-ray, or HD DVD will deliver reliable easy HD connectivity to your projector. Using the HDMI or DVI input on the projector makes the connection about as easy as you could ask for.
