Oh... now I see what the problem is. Actually this is not a real flat sun problem but more some weak halo effect. The 'real flat sun problem' is with Nvidia and shows just a solid disc instead of a sun with halo and rays. My 8800 GTS recently died so I know from experience. With Ati cards the rays look indead weak. Try this one and if you like it I will upload the others as well:
http://www.filefront.com/16045207/SH...default%29.zip
With Nvidia cards you will see a bigger halo and I expect it may even be uggly.
Rik