In the past I too have found in the that Maya and the catalyst drivers don't get on well together.
The image will look all aliased in the render view upon completion but if you save the image it will be fine in your picture viewer.
Also, I found that if you zoom in then out with the mouse wheel it will appear cleaner edged.
It's a bit of a pain but then again the Radeon cards aren't qualified for the software so there are going to be some glitches.
the main thing is that the actual render is fine, it's just the view in the render window that looks a little serrated
take it easy,