I tried the same thing multiple times, had a Nvidia G-Force PCI card in my machine. I got kmod-nvidia to work perfectly with all Fedoras up to 10, with 11 I never once got it working. Then I installed a new board, with ATI Radeon onboard sound, and couldn't get those drivers to work with 11 either. Do the install, and boot to a black screen. I wonder if I should try to install the drivers in 12? Did they get this issue fixed?
Here is a tip for you Fedora software coders:
There is a little distro named PC Linux, http://pclinuxos.com
which is RPM based and comes in Gnome and KDE. It has a little utility, in the utilities folder on the desktop. With this utility, you can easily install either Nvidia or ATI drivers, the correct ones, and it works every time.
Personally, I think Fedora would be great with this utility, how about the rest of you?