I installed Fedora Core 1 yesterday with a Radeon 9800 and had a similar issue.
The folks in Red Hat forgot that if you choose a text installation it is most likely because you don't have a compatible graphic card. If you reboot your system, it will restart in graphical mode (init 5) by default.
To solve the issue, I booted in rescue mode, mounted the file system (/mnt/sysimage) and changed etc/inittab to use level 3 instead of 5 (you may want to do that before rebooting after the installation).
Next, I installed the driver from ati, ran the fglxconfig and X is running just fine. I still have an issue with OpenGL support, which runs in software rendering mode. I contacted ATI about that issue though.
Good luck.