NVIDIA Driver Downloads - Advanced Search
177.39 with the following software will enable PhysX.
NVIDIA PhysX System Software
GeForce: 9800 GX2, 9800GTX, and GTX 280, 260
Video cards are reported to be supported. Driver 177.41
supports PhysX.
Andreas G. at Nordic Hardware has provided a list of 177.39 drivers that may,
at 29June08, be helpful with some 9XXX Cards.
NVIDIA ForceWare 177.39 beta with PhysX support