this is from http://www.fedorafaq.org/
Q: The installer's media check says all my CDs are bad!
A: There is a bug in the kernel which causes the media check to say some CDs are bad when they are not, on some systems. To do a successful media check, do the following:
1. At the installer prompt, type:
linux mediacheck ide=nodma
2. Run the media check on your CDs/DVD.
3. Reboot, and run the installer normally.