You must first install the kernel-headers according to your kernel version, as an example : kernel-headers-2.4.18-bf2.4.
You must now have a directory called /usr/src/kernel-headers-2.4.18-bf2.4 or something like that.
Now edit the file /usr/src/NVIDIA_kernel-1.0-4191/Makefile or wherever u put it and change the line:
or the correct path for kernel headers
now make install should work