Hey there. Check out my howto
for getting dri working with ati. Altho the new drivers work a lot better you might want to use the xorg.conf I have on the site.
When you install the ati proprietary drivers, you CAN NOT USE the desktop effects which comes with fc6. Ati has not put in support for aiglx yet so dont drive yourself crazy trying to get it to work. To use the bundled in effects you have to use the opensource driver but the dri (direct rendering) is slower then if you use the proprietary drivers. To test to see if you have direct rendering working you can issue glxinfo and look at the top for "Direct Rendering =" it will have either a yes or no. Um, an alternative to the aiglx which comes with fc6 would be to use xgl. Hope that helps. Let me know if you have any questions.