First you need to login into shell as root user than follow the steps one by one.

[root@gunjan]#mkdir /root/support  && cd /root/support

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/gmp-4.1.4-10.el5.i386.rpm

[root@gunjan]#rpm -Uvh gmp-4.1.4-10.el5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/readline-5.1-3.el5.i386.rpm

[root@gunjan]#rpm -Uvh readline-5.1-3.el5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/python-2.4.3-27.el5.i386.rpm

[root@gunjan]#rpm -Uvh python-2.4.3-27.el5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/libxml2-2.6.26-2.1.2.8.i386.rpm

[root@gunjan]#rpm -Uvh libxml2-2.6.26-2.1.2.8.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/libxml2-python-2.6.26-2.1.2.8.i386.rpm

[root@gunjan]#rpm -Uvh libxml2-python-2.6.26-2.1.2.8.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/expat-1.95.8-8.2.1.i386.rpm

[root@gunjan]#rpm -Uvh expat-1.95.8-8.2.1.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/python-elementtree-1.2.6-5.i386.rpm

[root@gunjan]#rpm -Uvh python-elementtree-1.2.6-5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/sqlite-3.3.6-5.i386.rpm

[root@gunjan]#rpm -Uvh sqlite-3.3.6-5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/python-sqlite-1.1.7-1.2.1.i386.rpm

[root@gunjan]#rpm -Uvh python-sqlite-1.1.7-1.2.1.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/elfutils-0.137-3.el5.i386.rpm

[root@gunjan]#rpm -Uvh elfutils-0.137-3.el5.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/rpm-python-4.4.2.3-18.el5.i386.rpm

[root@gunjan]#rpm -Uvh rpm-python-4.4.2.3-18.el5.i386.rpm

[root@gunjan]#It will throw following error.

[root@gunjan]# rpm -Uvh rpm-python-4.4.2.3-18.el5.i386.rpm

warning: rpm-python-4.4.2.3-18.el5.i386.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
error: Failed dependencies:
popt = 1.10.2.3-18.el5 is needed by rpm-python-4.4.2.3-18.el5.i386
rpm = 4.4.2.3-18.el5 is needed by rpm-python-4.4.2.3-18.el5.i386
rpm-libs = 4.4.2.3-18.el5 is needed by rpm-python-4.4.2.3-18.el5.i386

In that case search dependencies in following URL

http://rpm.pbone.net/

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/m2crypto-0.16-6.el5.6.i386.rpm

[root@gunjan]#rpm -Uvh m2crypto-0.16-6.el5.6.i386.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/python-urlgrabber-3.1.0-5.el5.noarch.rpm

[root@gunjan]#rpm -Uvh python-urlgrabber-3.1.0-5.el5.noarch.rpm

[root@gunjan]#wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/yum-3.2.22-20.el5.centos.noarch.rpm

[root@gunjan]#rpm -Uvh yum-3.2.22-20.el5.centos.noarch.rpm

It will throw following error.

[root@gunjan]# rpm -Uvh yum-3.2.22-20.el5.centos.noarch.rpm
warning: yum-3.2.22-20.el5.centos.noarch.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
error: Failed dependencies:
python-iniparse is needed by yum-3.2.22-20.el5.centos.noarch
rpm-python is needed by yum-3.2.22-20.el5.centos.noarch
yum-fastestmirror is needed by yum-3.2.22-20.el5.centos.noarch
yum-metadata-parser >= 1.1.0 is needed by yum-3.2.22-20.el5.centos.noarch

In that case search dependencies in following URL

http://rpm.pbone.net/

Once you complete all dependencies you can update yum by using following command

[root@gunjan]#yum -y update