From Fedora 12 nouveau interferes with the nvidia driver, to disable nouveau, first you'll have to blacklist it:
echo 'blacklist nouveau' >> /etc/modprobe.d/blacklist.conf
Open /boot/grub/grub.conf file and check that the kernel row have following parameters:
rdblacklist=nouveau nouveau.modeset=0
Reboot your computer.
This process involves the creation of a kernel module, meaning that everytime the kernel version changes (when doing a #yum update), you'll have to do it again.
To do this process I'm creating the directory /video/support/software/nvidia, then going into that directory and downloading the nvidia drivers with the wget command. Then I switch to mode 3, and perform the installation of the driver.
Once the module is built, switch back to run mode 5.
These are the commands:
mkdir /video/support/software/nvidia
cd /video/support/software/nvidia
wget us.download.nvidia.com/XFree86/Linux-x86/260.19.44/NVIDIA-Linux-x86-260.19.44.run
init 3
sh NVIDIA-Linux-x86-260.19.44.run
init 5
Once you are back in KDE, you can configure your graphics adapter by going to:
System->NVIDIA X Server Settings