If you want to use the graphic drivers provided by Nvidia, the easiest would be to install them via RPMFusion.
Using the .run installer from the Nvidia download page didn't work for me. There need to be too many manual changes to make it work properly.
Install the RPMFusion repository package from there website
Install the packages for your system
yum install akmod-nvidia
The akmod package should work with Fedora 15, too. If you want to use a prebuild package for your kernel, you can use the kmod-nvidia package. This package was not available for the Fedora 15 kernel at this time.
There is a prebuild package available now for the Fedora 15 kernel. Install the RPMFusion repository and then kmod-nvidia
yum install kmod-nvidia
It should work instantly after a reboot.