NVM I used the video guide and the Marathon spoiler website and got the achievement, I think the vid guide help more I think, not too long ago so the video guide pretty much works thank god. Your video guide was awesome by the way.
It's not the killing that's the only problem, it's surviving.
I love TA as well as xbox360achievements.
Games 100% Completed
I currently have 27 completed games according to TrueAchievements (25 retail and 2 arcade titles)