Well first let me say that you should not have updated the new kernel. If you looked at what the update was for, it was very unlikely that you needed it.
The easiest thing to do at this point is simply have grub boot from your old kernel. The problem is that you now have kernel *.19 and the rpm's were made for kernel *.18
so go to /root/grub/grub.conf
the default is probably 0 [default=0], for the first entry in it change that to a 1 and reboot.
You will always loose any kernel mods that you make. NVIDIA, ntfs support etc when updating the kernel. That is why it is not selected as a default in up2date.
So now wait until you see the rpm's for *.19 and them you can uninstall NVIDIA_* and reinstall in under the new kernel.
There are other ways to do this... But from what I'h hearing this is probably the best solution for you.