24 Oct 2008
This shouldn't be hard at all if you keep the difficulty low and the enemy density low. All you have to do is finish five levels.
If you have a friend on XBOX LIVE then this will prove even easier - as will turning Lone Wolf off if you are attempting it on your own.
However, If you are brave I recommend doing it in realistic as you can work towards the achievement for finishing all of the terro hunts on the hardest setting.