On Linux a new kernel version means that you need a new nvidia kernel module. You can do two things:
1) Don't use 2.4.18-5 since I don't think it is a that big update. Likely only a few bugfixes to some drivers.
2) Compile the nvidia kernel module for kernel 2.4.18-5. To do this download the nvidia kernel module in tar.gz or src.rpm format. Then make sure the development headers for 2.4.18-5 are installed. Then extract the source of the tar.gz version of the kernel module to a directory and do: make. If everything goes fine the new driver will be compiled and installed.
Or if you chose the src.rpm do: rpm --rebuild
file.src.rpm. (requires rpm development packages too) If everything goes fine an rpm package will be build. You can find the package in /usr/src/redhat/RPMS/i386 (or perhaps in another dir if it compiles for i686 for example)
Personally I would stick to the old kernel. The new kernel isn't needed. Compiling a new nvidia kernel module isn't something for your first/second day linux. (especially if the dev packages aren't installed and you need to install those by hand)