LOL - Yeah I seem to have forgotten. Anyway I just played through the first chapter in DX10 64-bit mode before posting this and it ran fine for me. Don't have my saves anymore to go to the chapter you're talking about so I can't check there, but again, I had no issues thus far.
Did you do what I suggested, which was make sure your drivers
are updated? Also make sure you update your DX files.
Let me know.
BTW we have the same card (6950), running at the same specs
I'm using the 11.6 Cat drivers.