Redhat EL 5.x is a propitiatory OS, and the only way
to have access to the repositories, is to get Redhat
support :
https://www.redhat.com/apps/support/
> > and "Register" to get the account.
.....
'CentOS 5.4' and 'Scientific Linux SL 54' are identical
free copies of Redhat EL 5.4 .
.....