You need to check the docs that came with for Linux distrib and see what they say about the kernel you have and then get hold of the source tree/header files for said kernel.
The reason for this is individual distribs often patch kernel ever so slightly before releasing them.
If all this fails you could get the latest source(*) and compile yourself a new kernel.
The latest 2.6 tree does not play well with the NVidia drivers when trying to install luckerly http://www.minion.de./
are happy to help