Sony and Nvidia have announced that they have been working together for the past 2 years on developing the graphics processor for the upcoming Playstation3, due to be released next year.
This may also be the reason the Microsoft announced some time ago (last year?) that they were dropping Nvidia in favour for ATI to supply the graphics processor for the new XBox2.
The role of the graphics processor in the PS3 is unclear at this point, as it is already known that the Sony/IBM/Toshiba designed and produced Cell processor which is going to be at the heart of the PS3 is going to incorporate advanced processor capabilities for processing vector graphics and graphics processing.