I heard from a friend that there is a way of hex editing or some sort of hacking that makes it possible to play the campaign maps on halo to system link games, as long as all of the boxes on the system link hacked the game as well. Well anyways I have tried google searches, but can't seem to find anything on this. If anyone knows what I am talking about, or kowns something else similar to do, please help me with anything.
Thanks
Brad

No, it's not possible. There is no system link coop play and there is no mp in sp levels. The only thing even close in MonoxideC's multiplayer map that was made using the Library from single player, but that was for Halo PC and was extremely difficult to make and needs map rebuilding, which is currently only possible using Halo Map Tools and does not work for the xbox version yet.

can this be done yet?

quite a lot of single player maps have been converted for multiplayer death matchs, but no system link single player as of yet.