My desktops and laptop are Ubuntu boxes, but I'm working on manufacturing a Fedora-8 based product, so I've spent a couple of weeks at work learning about various aspects of the Red Hat Package Manager (RPM) and the Yellow Dog Updater (Yum).
Documentation is sometimes spotty, sometimes out-of-date, and sometimes absent.
Here, though, is quite a nice post on how to set up a local yum repository.
It's missing a createrepo in the step on how to set up an updates directory, the directory that mirrors Fedora's new and updated packages. However, that step's completely analogous to the earlier step for the Everything directory, which holds all the RPMs from the original distro, and the error message I got when I left it out was helpful.