There's also False.Genesis' build, with his experimental mod selection page, found here. His build contains all the patches post-achurch merge. I would recommend you use his build, because it's more up to date.
Uh oh. If you do, be sure to look out for updates here and there, as said in the other topic, this build is highly experimental, and likes to go kaboom, especially when quitting.
I'll update that from time to time and eventually throw out an update for everyone, when its done, stable, and tested enough.
Something else random i found related to your problem:
I bought this great game today and had the same graphic issue, but I found how to fix it or at least it worked for me.
My graphic card is also x1950xtx so this surely is x1xxx problem or just ati driver problem.
But about the fix, I tried every settings both game's and catalyst's.
So these are the configs that worked for me:
On catalyst 3D:
- set every setting to " use application settings"
- disable catalyst A.I.
- mipmap detail level: performance
- wait for vertical sync: Off, unless aplication specifiec
- adaptive anti-aliasing: off
- Triple buffering: off
For the game settings: enable Vsync and frame buffer effects.
You can also try decreasing resolution or try windowed, but for me the game's default settings worked fine after setting catalyst right.
Hope this helps people who still have old ati card 
But this post is kinda old and probably outdated.
For the record, i never had problems running the game, it was *almost* playable on that 800 MHz machine, and it ran fine everywhere else, including an older Pentium4 machine, another old Pentium 4 Prescott one with an Ati all-in-wonder-something, my C2D/GF8800GTS Desktop, and my C2D/GF9800M GTS Notebook.
You have really bad luck it seems...
Eh, tried disabling framebuffer effects? Thats the only thing that costs a lot of performance, besides the screen resolution.
EDIT: Don't forget posting your config! xD
