Please try on other computer with CD driver to read that burning CD with RH.
If it works then try to download again that ISO cd's.
It happend to me but with Mandrake 8.0 .
The same Nero but with a Copy-CD not ISO burning.
The result was that the cd was unreadeable in RPMS directory.
I don't know what was the problem ...
Sorry for my english.
Regards.