1. All Dish Network STB's have analog SD outputs, so an HD box can be connected to an SDTV using one of the analog outputs. So, the HD is already down-converted for you via the analog outputs (S-Video or composite or component at 480). While the down-conversion won't be in HD, the PQ will be better than the SD equivalent channels.
2. I believe that Dish does, in fact, open all the SD equivalent channels of the HD only packages. So, you would, in fact, have the SD feeds as well as the HD feeds. Dish unlocks the SD equivalents because some people have the old Pocket Dish or the Archos recording devices that can only have SD input to them (there is supposed to be a model very soon that can handle HD input) and the SD channels are also opened to allow you the option of recording to DVR the SD channel for some programs (such as talking head shows) so that you can save space on your DVR for more HD recording.
Of course, this is if Dish is installing you, then you will be looking at satellites for both the SD and HD channels. If you are the Eastern Arc, you will be looking at 3 sats for SD and HD or at the at the Western Arc, 3 satellites for SD and HD. This is the standard install for HD now. This is how Dish wants all installs to be even if you are subscribing to even an HD only pack. It gives Dish flexibility to move channels around the 3 satellites for greatest efficency without you losing any programming. However, for someone else subscribing to SD packages only, then Dish installs, in most cases, only what is necessary to receive the SD channels only. When that person is ready to subscribe to HD, they will have to pay the upgrade to look at the sat that has most of the HD on it.
I hope this answers your concerns. Don't worry, you will have the ability to do what you want to do.