Well for all those who have used Nvidia cards for PhysX and ATI cards to render graphics in Windows 7, that is about to change.
Since the release of 186 graphics drivers Nvidia has decided to disable PhysX anytime a non-Nvidia GPU is even present in the same PC. We do feel that Nvidia has shot themselves in the foot here.
In NVIDIA's defense, they have been saying ever since the beginning that they would not support the ATI / NVIDIA combo PhysX wise, it is now a little more definitive though.
Small advise to NVIDIA, PhysX will be a lost cause unless you guys get ATI onboard as well. This certainly isn't helping.