Download the latest perl-Curses for your build from http://dag.wieers.com/rpm/packages/perl-Curses/ using wget
At the time of this How To it is: perl-Curses-1.23-1.el5.rf.x86_64.rpm (64bit) or perl-Curses-1.23-1.el5.rf.i386.rpm (32bit) for CentOS 5

wget http://dag.wieers.com/rpm/packages/perl-Curses/perl-Curses-1.23-1.el5.rf.x86_64.rpm

Install the RPM:
# rpm -Uvh perl-Curses-1.23-1.el5.rf.x86_64.rpm

Download and Install mtop from http://dag.wieers.com/rpm/packages/mtop/ – Again, select the appropriate version
# wget http://dag.wieers.com/rpm/packages/mtop/mtop-0.6.6-1.2.el5.rf.noarch.rpm
# rpm -Uvh mtop-0.6.6-1.2.el5.rf.noarch.rpm

Execute mtop
# mtop