Hello everyone. First of all, this is my very first post here and being a forumnab and my engrish frankly svcks, so might be confusing but bare with me on this
I recently found a thread in http://www.xtremesystems.org/forums/showthread.php?273794-Enable-FXAA-in-Dx9-Dx10-and-Dx11-Games-Now-by-some-dude!-Version-9

from what I understand it is a new type of antialiasing that is currently only cpu based (?). I just now tested it with Oblivion and least to me gave free AA with no performance loss. Provided I first disabled the AA settings from the nvidia control panel (should work with Ati as well)

I suggest you check out the thread linked above and see for yourself it has any difference. there is a link for the file and it consists of 4 files that go into oblivion base folder so its simple to try out. Just wanted to share this since it seems promising and also it is currently in version 9beta and being regularly updated.