How about an explanation with those links.
EDIT: Or I guess I can just download it and find out what it is...
Its a PDF file titled "NVIDIA Physx Reviewer's Guide" and it seems like a pretty comprehensive overview of what Physx on the GPU is all about.
I found one interesting bit of info so far:
Delivering physics in games is no easy task. PhysX technology is an extremely
compute-intensive environment based on a unique set of physics algorithms that
require tremendous amounts of simultaneous mathematical and logical calculations.
This is where NVIDIA GeForce
processors come in. With the NVIDIA GeForce
177.79 driver, GeForce 8, 9, and GTX200 Series graphics processors become
physics processors too. A driver supporting PhysX on these products will be made
public by August 12, 2008.