I followed the instructions in this thread to install nvidia graphic drivers, but failed miserably. The error message tells me to look at /var/log/nvidia-installer-log, but that doesn't help me very much either. What's sure is that it fail to buil the module and that the kernel has nothing pre-compiled for the nvidia driver (??)

I was wondering (apart from who could give me a quick and easy sollution) whether this might be in any way related to having the kernel source installed. rpm doesn't tell me I have it, and I'm unable to find it on the DVD. Where is it? Do I need it?

Yes, you DO need the kernel source installed! If you have internet access, you can just go to www.kernel.org and download a kernel source, and unpack it (it could take a little while). The kernel source is usually placed in /usr/src, but you should be able to place it anywhere so long as you tell the nvidia installer where it is located (I believe it only checks the /usr/src location). Once you have unpacked and placed the source folder, try to install the nvidia driver again.

it provided with the distro???
Just to make sure, I suppose I need to

$ rpm -q kernel

and download a source that matches it exactly.
Does it need to be an FC· package?

It used to be provided with fc1 and fc2 but it is not provided with fc3, which is why you need to get it from www.kernel.org. It does not have to be an fc package (rpm) nor does it have to be the latest kernel source available. For example: I am running fc3 with an nvidia GeForce 5700LE on a dual monitor setup. The fc kernel is 2.6.10-1.741_FC3 yet the kernel-source that I use is linux-2.6.9, which was a tar file. I downloaded it from the website, and unzipped it and placed the unzipped folder in my /usr/src directory then followed the instructions to install the nvidia drivers.

Thanks for the info ..I'll get to it

I'm a little puzzled though that I can use a kernel-source which doesn't coresspond to the kernel I'm using. Would anyone care to explain?

$ rpm -q kernel
kernel-2.6.9-1.667
... so I've decided to download linux-2.6.9.tar.bz2
I saw thre's a .sig file available. Can you tell me how to use it?

That .sig file shouldn't matter. I never had to do anything with it to get my nvidia drivers to work.

the reason that you can use a different kernel-source from the kernel that fedora is using is because the kernel-source file is for compilation purposes. Fedora is already compiled using whatever kernel it is running on, but if you wanted to recompile the OS (to add or remove features, etc.) then you would use the kernel-source that you downloaded to compile a new kernel (which in your case would be 2.6.9). If you did all of the compilation steps already, then when you restart fedora you will be able to run it under your newly compiled kernel.