kernel-source2.4.20 is what you should look for in your cd. Again, I believe there should be a release number with it..i wonder why it isnt showing up. Without that you wouldnt know which one to download.
Do, uname --help for help on this topic. You can find source rpms here:
if all fails then install x and gnome and do the steps I told you. You can always uninstall it .
Hope it helps