Standalone module - you downloaded ftpfs-x.x.x-k2.4.tar.gzIn order to build the module, you need to have the kernel headers installed. All distributions install the headers by default. The latest however, seem to install some weird headers which cannot be used to build modules. In this case I recommend using the original kernel headers, or better yet, recompile the kernel with FTPfs support using the kernel patch.
Also make sure you have the package corresponding to your kernel version (ftpfs-x.x.x-k2.4 for kernel 2.4). The 2.2 branch is dead so I strongly recommend you update to 2.4.
Executing make install as root, in the directory where you uncompressed the archive should build and install the ftpfs.o module & ftpmount.
The kernel patch - you downloaded ftpfs-x.x.x-k2.4.x.patch.gzAs I'm sure you know, you need the kernel source. Suppose it is installed in /usr/src/linux/.To apply the patch:
cp ftpfs-x.x.x-k2.4.x.patch.gz /usr/src
cat ftpfs-x.x.x-k2.4.x.patch | patch -Np0
Next you configure, compile & install the new kernel. For instructions, please consult a more reliable source. Don't forget to enable FTPfs support when configuring the kernel (File Systems/Network File Systems).