If you are leasing any Dish HD equipment you must subscribe at least to the HD Pak. It is free for the first six months. Then it $9.99 after that. If you own your equipment you do not have to subscribe to an HD pak.
My understanding is that you must subcribe to one of the 'America' packs to qualify for leased equipment. This is what I was told by the reps I talked to. I had to send my leased receiver back when I decided to cancel my top 120 pack and keep only the HD Package and Voom (and one Brazilian channel).