Well, few days after 2.6.26 released, finally NVidia released a new driver which restores the compatibility with the kernel. In fact, i was one of the victim who ran into a problem when i tried to upgrade my kernel and compile my NVidia driver. It won't compile, since the changes in the kernel broke the driver.
Well, at least they have fixed it now and it should work on 2.6.26 also. Here's the information page: