If you face the Media Check Failure for Disk2 and Disk3 of Fedora Core3 and be adviced by the Media Check Tool as it would not be safe to continue installation, don't despair! Yeah, I understand the frustation caused when you try to install latest FC3 after a download/ purchase.
But remember that you are not alone, Bugzilla Bug#139213
This is a not a Real Problem, your media is proper and you will be able to install the system completely.
The issue here is, during the install DMA ( Direct Memory Access) mode is entered for faster installation ( + others) and Installer is trying to communicate with your Devices directly and your CDROM did not have a proper DMA working and hence this result. ( this is what I came to know,references below)
So to solve this problem,during the Installation, give:
Now you might find that CD2 and CD3 Media check Passes!
Refer the following for some discussions: