This package; sk98lin-8_13-rh3-2.4.21-40.EL.i386.rpm is not built for FC5 or any other version of Linux except for Red Hat Enterprise Linux version 3 with kernel 2.4.21-40 installed. Remove it, it will and does not work any how. It was built for a 2.4 kernel not a 2.6 kernel.
Why not use the sk98lin module built (as part of the kernel) for FC5??
First it may have been detected and the module is loaded;
cat /proc/modules | grep sk98lin
Quoting from the /usr/src/linux-2.6.XX/Documentation/networking/sk98lin.txt file;
This should produce an output containing a line with the following
eth0 eth1 ...
which indicates that your adapter has been found and initialized.