one... FSAA does NOT stand for FULL SCREEN ANTI-ALIASING... it stands for FULL SCENE ANTI-ALIASING. Given this ANY technique which applies itself to the entire scene is FSAA.
MSAA == FSAA (essentially edge detection using delta Z calculations, expensive on Zbuffer but not on the color buffer)
SSAA == FSAA (essentially X times more resolution on the front buffer, expensive overall, provides the best results but costs a phenomenal amount of GPU power)
secondly - while I can't reveal the requirements for xbox 360 I can tell you this...
a game running in 720p without AA at all looks fantastic,
a game running 2xFSAAx720p looks better, smoother...
a game running 4xFSAA looks marginally better.
a game running in 720p applying full screen motion blur, bloom effects, Depth of field and also using FSAA looks amazing.
stop complaining... stop guessing.... we're not allowed to tell you whats required, whats happening or what will happen. Look, see, absorb and marvel and how smooth things look when done correctly.