It's actually not a standalone driver. It's the newest PhysX software, but it doesn't contain any drivers. Any computer can run the software and use the CPU for PhysX calculations, but any game would be crushed by the pressure it puts on it.
However, Windows XP and 7 are able to use two different graphics drivers at the same time, and I've seen benchmarks to go along with it. It's too late for me to pull up all the information that I've found so far, but I ordered me a 9500GT yesterday to take a shot at it (I'm running a 4830 currently).
The process in which to get it working has seemed difficult, but I'm gonna toy with it and see if I can get it to work as others have. And you can bet your sweet behinds that I'm gonna post benchmarks, because I'll be damned if I can't get it to work!