Ok another pet peeve is the Xbox 360 and "backwards compatibility". If it were so easy, MS would have touted it from the start - major selling feature, something you would not forget to mention. It's not though because of the move to Ati/IBM, but after everyone was quick to go "oh.... it may not be??..." after the MTV event, they were quick to respond with... oh wait it is..... kind of, for select games.
Then the, "See, emulation!" started to arise. However you don't emulate with any efficiency in this environment....
Rather, I can almost 100% guarantee this is the way it's going to work.
Certain games of choice (::cough:: halo for one) will be ported to the 360 - basically anything that is platform dependant... what's not platform dependant you say? Your textures, maps, etc... That information will be obtained from the original xbox game disc. So you download this "port/re-release" to your 360 most likely via your Xbox Siver (or if they want to get cute, paying Xbox Gold) account. In order to play the game you still need to insert your original xbox game disc. This method would allow them to provide the downloaded content _free_ since you need the original game disc, thus proving you own the original title.