No it is not possible.
They didn't do system link co-op on either Halo CE or Halo 2.
"slug" <slug.RemoveThis@go.cc> wrote in message
news:116gj58ak46ke63@corp.supernews.com...
> Does anyone know if it is possible to play a 2 player campaign using 2
xbox
> systems on halo or halo 2.
> If possible please explain.
> I would really appreciate it.
>
>
> >> Stay informed about: Halo 2 player campaign