There are many variables with the Radeon and flicker problems, but heres my story.
I bought a Radeon 64 to use with my NEC 21" E1100 monitor, No matter what adapter setting I used I had constant flickering problems in all MHZ ranges. ATI was playing dumb and dumber and they even sent me unreleased drivers to try to rectify this flickering problem.
Unfortunatly nothing worked and I replaced the card with a Geforce2 Pro and now my monitor flickers no more.
Im sorry I couldnt help you out, but the Radeon and NEC large monitors to not mix well together in my situation.
I noticed Flicker problems, er tiny white specks, when I ran 3dmark2000, but not 2001. I have not noticed this in any other game or program. Thinking back on it, I used the radeon tweaker to change a setting that made it go away, but im not sure which setting it was.
SO damn, I guess im not much help, why did I bother to type this>? LOL
Seriously though, get the Radeon Tweaker program, and play with the D3D settings.