locate and install the kernel sources relative to the kernel you are running now.
The absolute only place I can find the sources for this kernel is here.
http://rpm.pbone.net
type in the search bar,
kernel-source-2.4.20-6.i386.rpm
and search there will be downloads for this rpm package.
install it with
rpm -ivh kernel-source-2.4.20-6.i386.rpm