If you want low cost anti-aliasing that doesn't destroy performance, try this InjectSMAA hack. You must disable the steam community overlay or it will mess up the graphics.

It is a post-process AA similar to FXAA, but it doesn't blur textures.

http://forums.nvidia.com/index.php?showtopic=207106

http://mrhaandi.blogspot.com/p/injectsmaa.html