The nVidia cards are noted for problems with B&W but seldom the ATI ones.
Which driver version do you have for that card? (Start > Run, Type in dxdiag and click on the video tab)
I've always played B&W using the Radeon cards without a problem. I just got a new PC, which like yours, is PCIe rather than AGP and a X1900 graphics card. Since hadn't played B&W on it yet it I thought that might be the problem. So I loaded the game up and tried it unpatched, (damn tutorial) then with the V1.10 patch and then finally the V1.20 patch and my profiles. Everything worked as expected without any graphical problems or crashes.
Have you tried the V1.20 patch?