anti-aliasing is not done in shaders. you could still do some blurring with a post-processing shader, but you'd need a7 for that. i'm not sure if there are some kind of per-object blurring shaders - maybe with a vertex shader similar to one of the fur shaders.
Why not, just render everything bigger in a target and run a postprocessing shader that scales it down to the selected resolution with a sophisticated algorithm.
