You will need to build rpms from source or use the tar.gz source files.
Anytime you have Nvidia drivers installed and upgrade to a newer kernel from up2date you need to reinstall the nvidia drivers because as neo said they were compiled for a different kernel.
The next time you boot, let x go through its ritual of flashing at you when it stops, just hit the enter key, that will give you the log in prompt.
Log in as root, and type mcedit /etc/X11/XF86Config-4
You will now be able to edit your XFconfiguration.
Just comment out the changes that were needed to get the nvidia drivers going, and change "nvidia" back to "nv"
Hit F2 to save and F10 to exit, you can now reboot shutdown now -r
When it boots back up yopu will have the generic drivers again, and be able to use the GUi to do what you need to do for the new drivers.
To make a set of rpm's for the new kernel download the new GLX and kernel files in the src.rpm files.
Then for each one of them, type rpm --rebuild NVIDIA_GLX-*****.src.rpm
Of course sub the real file names in there
the new rpms will be placed in /usr/src/redhat/RPMS/i386
Those are the ones that you will install, either by clicking on them or from the command line.
You will then need to change the XF86Config-4 file back to use the 'nvidia" drivers.
Reboot and all should be fine.
I am certainly no expert but this works for me, and just did it yesterday on three machines after getting the newest kernel at up2date.