correct CentOS is NOT supporting 4 any longer
and 4.8 went end of life with centos 4.9
currently CentOS is ONLY supporting CentOS 5.9 and 6.4
basically there is nothing to install on 4.8
i am guessing that yum was installed before it became unsupported
if not CentOS 4 uses " up2date" like RHEL4
There is not option to upgrade
so a new install of CentOS 6.4 is required
but if you NEED centos 4.8 for some legacy software that is NOT supported in RHEL5 or 6
then you can use " The Vault"
if yum is installed ????
then you can point the cent.repo to " http://vault.centos.org/4.8/"
but it STOPPED getting updates back in May of 2012
with the "extras repo in mar of 2010
the "CentOS-Base.repo" file in the 4.8 vault folder POINTS to centos 4.9 !