I have a feeling it might be the CD, too. I'd atleast try burning the ISO again before worrying about other problems.
CD burning has come a LONG way since I got my first CD-R drive, but problems still come up!
You MIGHT even be better off grabbing the ISO again to make sure that nothing was corrupted during transmission (TCP/IP is damn good about error correction - but once again it's not unheard of to have those problems).
Better yet, go buy a boxed set and support RedHat.
It very well might be a different problem, but before we delve into those I think it would be safest/best to get those potential issues out of the way.