As recently reported, AMD's new HD 4000 series is supposed to be capable of physic calculation - until now it was unknown how this was supposed to work.
Havok: Working together with AMD
Now AMD announced cooperation with Havok. But the developers of the Havok Engine were bought by Intel only last year and thus belong to AMD's competitors. Intel didn't comment to the situation, yet. According to AMD Havok's physics engine is scaling very good with AMD's products. And still a support for Nvidia's PhysX via CUDA is not excluded, but isn't planned for the near future.