I've created a few functions to be used with pygame which are based on anti-aliased curves. At the moment and likely forever, it has two useful functions:
Draws an anti-aliased circle on the surface s at the starting point x and y with the radius r. The circle will be coloured with the colour parameter which takes the usual colour tuples eg. (160,200,255).
Takes the surface s and creates rounded corners with the radius r. The corners are anti-aliased. Please not due to a problem with pygame's aaline function, 2 pixels will be cropped from the top and bottom and 1 pixel with be cropped from the sides.
Run the library directly to load a demonstration. You should get http://www.godofgod.co.uk/my_files/curvelib.png
It's been tested on Mac OSX 10.6.1 Snow Leopard