Your AA is set too high, thats why you have triangles.
Sometimes, less is more.
Install this:
http://www.nvidia.com/object/winxp_169.21_whql.html
Anisotropic Filtering at 8x (though I actually prefer mine at 4x), and then put your Antialiasing to 4x.
Set it to run on 'Hardware' and not 'OpenGL'.
Problem solved.
I run SH3 on a P4 2.4 Ghz, with 1.5 GB RAM, using an Nvidia 7300 GT... and it looks beautiful.
That should take care of the flickering.
Enjoy.
Ps. I know you're looking for ATI card suggestions... but I thought I'd let you know that little trick first.... because I ditched my ATI 9600 for the Nvidia 7300, and haven't looked back. (ancient computer - bah)
I haven't been lurking around here too long, but Nvidia seems to be the dominant / preferred card brand.
If anything, look at a higher end Nvidia card.
I believe the 8800 GT is the best deal price-wise at the moment...
... but if you are serious about your games, check this out:
http://www.canadacomputers.com/index...017704&cid=999
It's a pair of Nvidia XFX GeForce 9600 GT's.. a friend of mine just got this and put it in his new machine....
... and I can state without hesitation that it is, in fact, the cat's ass.
Good luck.