Sorry for the misunderstanding.
I had Live only for the XBox 360. Tho you could always log into your Live account via your old XBox.
Anyways, I played Halo 2 on my 360. But I use to play Halo 2 years ago on my original XBox as well.
They threw me a bone despite being on Live since the first year of It's released.
It's just that simple.