The problem is just what it says, CUDA isn't supported on Fedora 15.
That's why the Fedora version mentioned on http://developer.nvidia.com/cuda-toolkit-40
is Fedora 13.
The main issue is the compiler in Fedora 15 is gcc 4.6 but CUDA 4.0 needs gcc 4.5 or lower. There are several options
1) get the gcc source from gcc.gnu.org for one of the older versions like gcc 4.4, build that and use it for building CUDA software instead of the official Fedora 15 gcc compiler. I did that at work so I could use Fedora 14 with CUDA 4
2) the hack way:
go in /usr/local/cuda/include/host_config.h and comment out the testing code there around line 82 that detects your compiler version and stops the compile. I think this mostly works because the problem with gcc 4.5 and higher is doing something that the cuda debugger can't deal with. But if you never use the debugger it won't matter. Eventually cuda will catch up to gcc.
3) use Fedora 13 or other supported linux