感谢网易的同学，速度很快，配置文件如下。
如果强制使用5的源（用于升级系统到centos5），如下：
[base]
name=Base
baseurl=http://mirrors.163.com/centos/5/os/i386/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[updates]
name=Updates
baseurl=http://mirrors.163.com/centos/5/updates/i386/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[addons]
name=Addons
baseurl=http://mirrors.163.com/centos/5/addons/i386/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[extras]
name=Extras
baseurl=http://mirrors.163.com/centos/5/extras/i386/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[centosplus]
name=Plus
baseurl=http://mirrors.163.com/centos/5/centosplus/i386/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
强制4，则如下：
[base]
name=CentOS-4 Base
baseurl=http://mirrors.163.com/centos/4/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[updates]
name=CentOS-4 Updates
baseurl=http://mirrors.163.com/centos/4/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[addons]
name=CentOS-4 Addons
baseurl=http://mirrors.163.com/centos/4/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[extras]
name=CentOS-4 Extras
baseurl=http://mirrors.163.com/centos/4/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[centosplus]
name=CentOS-4 Plus
baseurl=http://mirrors.163.com/centos/4/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
如果根据系统使用源，则如下：
[base]
name=CentOS-$releasever ¨C Base
baseurl=http://mirrors.163.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[updates]
name=CentOS-$releasever Updates
baseurl=http://mirrors.163.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[addons]
name=CentOS-$releasever Addons
baseurl=http://mirrors.163.com/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[extras]
name=CentOS-$releasever Extras
baseurl=http://mirrors.163.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
[centosplus]
name=CentOS-$releasever Plus
baseurl=http://mirrors.163.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
