Posted by: JacobGRocks
It's ok. Just do this:
Copy the first SP map (the herectic cutscene level), and make copys of it with names of all the other SP maps. Now do it on legendairy. Boom, almost all campagin achivements. Enjoy your gamerscore without xlive achiever.
Ironically, I did that right after I posted this topic. Like hell I'm going through it again, it was pretty boring anyway.