2012년 초부터 CentOS 4.x 버전의 yum mirror 주소가 mirrorlist.centos.org 에서
vault.centos.org 로 변경 되었습니다.
따라서 /etc/yum.repos.d/CentOS-Base.repo 파일 내용을 아래와 같이 바꿔줘야 합니다.

# vi /etc/yum.repos.d/CentOS-Base.repo

[base]
name=CentOS-$releasever – Base
baseurl=http://vault.centos.org/4.9/os/$basearch/
gpgcheck=0
priority=1
protect=1

#released updates
[update]
name=CentOS-$releasever – Updates
baseurl=http://vault.centos.org/4.9/updates/$basearch/
gpgcheck=0
priority=1
protect=1

#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever – Addons
baseurl=http://vault.centos.org/4.9/addons/$basearch/
gpgcheck=0
priority=1
protect=1

#additional packages that may be useful
[extras]
name=CentOS-$releasever – Extras
baseurl=http://vault.centos.org/4.9/extras/$basearch/
gpgcheck=0
priority=1
protect=1

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever – Plus
baseurl=http://vault.centos.org/4.9/centosplus/$basearch/
gpgcheck=0
enabled=0
priority=2
protect=1

#contrib – packages by Centos Users
[contrib]
name=CentOS-$releasever – Contrib
baseurl=http://vault.centos.org/4.9/contrib/$basearch/
gpgcheck=0
enabled=0
priority=2
protect=1