Apt-get install the linux-headers belonging to your kernel. Kernel headers version must have exactly the same version number as your running kernel.
gives you this version.
Go to nvidia.com and d/l the latest legacy driver which supports your GPU. Especially if you are running kernel 2.6.26 it MUST be the latest, otherwise it won't compile.
substitute jadajada so the correct file name is called. If it fails, post back, including the error log which shows up in /var/log/. Later when I am behind another machine I can check the correct version number of that legacy driver.