You can force the install by doing this:
rpm -iv kernel-2.6.7-1.494.2.2.i686.rpm --force
Don't forget to uninstall the nvidia drivers by doing this:
edit your /etc/X11/xorg.conf back to default or X won't load:
boot the kernel-2.6.7-1.494.2.2
and install the nvidia again.
It is a good habit to keep a second kernel in GRUB, for this kind of situations.
Good luck! Any questions, just post them!