Heyyo,
Yeah, I was highly upset when gearbox made up the excuse of not including coop cause "the AI's too advanced," and "the AI wouldn't handle internet lag properly." BS eh? I mean, Far Cry has a much more advanced AI than Halo, and it has a coop mod. But yes, technically, it is possible to have Coop on HaloCE (the custom edition) cause I've seen some mp maps that they just put on some SP bots onto and just tweaked n' it worked... sortof.
Eventually I bet someone with good bot/networking knolege will use HEK (Halo Editing Kit) to convert some SP maps to MP.
