Though new 3dfx drivers (story) were released since the mention of problems with 3dfx hardware and the Soldier of Fortune Demo in Rick Johnson's .plan (story), a subsequent message from 3dfx Interactive's Developer Relations Manager Keith Galocy gives word there are still some known issues (so it's not just you). Here's the skinny:

3dfx has been working with Raven to fix a bug found in our OpenGL ICD. We didn't get the problems fixed in time for the driver release that went up today but we will have an update soon. Please post the following message so 3dfx users recognize that any anomalies they see in the demo are going to be fixed and are not Raven's fault:

"Some users may experience graphical glitches using a 3dfx card with the Soldier of Fortune demo. 3dfx is aware of the problem and we are working closely with Raven Software to correct the issue. We expect to have a fixed driver shortly. We are sorry for this inconvenience and would like to thank Raven Software for their patience and cooperation."