Do you get Xbox 360 gamer points playing an original xbox game on an xbox 360?
Unfortunately no you don’t. As the Gamerscore is encoded into each game disc this would mean every single original xbox game would have to be re-mastered. Although Microsoft did express some possibilities of this happening for a select few games (Halo: Combat Evolved for example) whether this will actually come to light is another matter. Simply put, they are fun to re-visit but won’t earn you gamerscore. Hope this helps!