Try playing the game without Physx installed and it won't work at all. Physx works in one of two ways,
1. GPU assisted Physx which only works on Nvidia cards, and the game must have been coded to use it as well.
2. Software Physx which is used on any video card, or if the game wasn't written to use GPU assisted Physx.
According to here, PhysXInfo.com - Projects using PhysX SDK
this game only uses software Physx regardless of which video card is used. Might want to make sure you have the latest drivers
for your card, Latest AMD Catalyst Video Driver for Windows 7
the latest Physx software, NVIDIA DRIVERS 9.10.0513
and the latest DirectX is installed, Download Details - Microsoft Download Center - DirectX Redist (June 2010)