Ah, OK. I say this so many times that it gets a little tedious after a while, but oh well.
Actually, kernel-source isn't your only problem. But install that first -- put in your Mandrake CD 1 and reboot to the installer. Go through the installation, choosing everything the same as you did the first time, up until it asks whether this is an install or an upgrade. Hit upgrade there. Again, choose everything the same as last time (your last choices should be the defaults now, but I'm not sure) until you get to package selection. The easiest way now would be to select the development meta-package, but it is possible to hit "prompt individually", hit the "flat view" button, scroll down to kernel-source-<version>, and select it. Also make sure that "make", "gcc", and some other packages are installed, though I'm not positive which ones. That's why it's often easier to select the whole development meta-package instead.
Continue on until it's done copying files, then exit the installer (hit the star over on the way left next to the last installation step, and that should do it). Take out CD 1 if it's still in, and reboot to your Mandrake system.
Now, I'm also seeing this in the compilation command:
-DNV_MAJOR_VERSION=1 -DNV_MINOR_VERSION=0 -DNV_PATCHLEVEL=4180
which means that you're trying to install driver 1.0-4180. This is almost assuredly not
the correct one; 4191 is the one that 99% of people should be using. Let me put it this way -- if you don't know what AMD64 and/or IA64 are, exactly, then you need the IA32 driver, which is in release 4191. Even if you have an AMD chip; the AMD 32-bit chips are still IA32 compatible.
So go back to the download page, and select linux ia32 instead of AMD64 or IA64 or whatever you selected last time, and download the proper NVIDIA_GLX and NVIDIA_kernel tar files for that version.
Now, I'm not sure on whether Mandrake's kernel-source is configured properly or not (I think it used to be, but I'm not positive, and it may not be anymore). So if you get other errors after all this, try going into /usr/src/linux and running a make mrproper oldconfig dep
(AFAIK, the proper .config file is in /usr/src/linux; if it wasn't, you'd have to find it and put it there). If that doesn't help, try a make clean in NVIDIA_kernel, then if even that doesn't help, post the errors you're getting.