I've read about where deleting or renaming atimgpud.dll fixes the flickering....sort of.
Don't do it!!!! ( just yet )

Go to mydll.com website...find and download atimgpud.dll...unzip , open the folder and scroll down to you see the 64 bit version of the atimgpud.dll library...copy and paste that file to desktop.

Now go into the Fallout folder....rename the atimgpud.dll ( to anything )..now take the one you pasted to desktop and drop it in there....simple as that. ( leave the new dll. name alone...it should read atimgpud.dll )

You are simply replacing the dll. library

Worked like a charm for me..I was having HDR flickering and water reflection weirdness ( water turned all green when I got near it )

If the sky is too bright...simply open the Falloutprefs folder under My Games in Document and Settings and scroll down till you hit sky brightness and change it from .5000 to .1000..( or whatever knocks you out) ....it's towards the bottom.

But I didn't have to do that either...

I just simply downloaded the new library and replaced the default one....works great !

Now if only that worked with Nvidia...........