According to current plan, confirmed by high ranked Nvidia executives, a driver that will drive PhysX on Geforce 8 and 9 GPUs will come at least a few weeks after announcement of GTX 280.
Geforce GTX 280 and 260 are about to launch next week but the PhysX driver will follow a few weeks after. Nvidia simply wants to be ready and as you know Nvidia uses its CUDA marchitecture to make this possible.
We were informed that all the PhysX enabled games including GRAW and Unreal tournament 3 will work with PhysX over GPU and you won't need Ageia card anymore to get the benefits. It will be interesting to compare the performances fo Ageia card to the actually Geforce PhysX scores.
At this point the driver should be out at some point in July if it doesn't hit some further delays.