FXAA does AA on the whole screen image instead of 3D objects. It does it after the frame is already rendered so it's not as good as regular AA but it is way faster than old fashioned AA
As for the profile conflict see this:
http://forum.1cpublishing.eu/showthread.php?t=29019
I already submitted a request to change the games .exe so the average joe doesn't get screwed up by Nvidia profile conflicts