Just a short note from Fedora Core 1 on a box that was previously RH 9. Upgrade steps are simple -- no CDs necessary, no reboots needed other than to bring up your new kernel.
Install Yum. Edit /etc/yum.conf to point to a Fedora mirror (use Gilbert's patches, but change $releasever to 1) Run "yum upgrade" Reboot into your new kernel
That's a bit of a stretch. I had to delete one rpm that was causing a dependency failure, but it wasn't necessary anyway. I also had to edit /boot/grub/grub.conf to default to the new kernel (not sure if that was the upgrade that defaulted it to the old one). And, more strangely, my eth0 didn't work even though it was detected (wouldn't receive packets even though they were being sent). eth1 worked fine, though. I noticed Fedora has some hardware management stuff that comes up on boot, this behaviour is classic interrupt stomping.
Enjoy.
Sean