For CentOS 32bit:
rpm -i http://dag.wieers.com/rpm/packages/unrar/unrar-3.7.4-1.el5.rf.i386.rpm

For CentOS 64bit:
rpm -i http://dag.wieers.com/rpm/packages/unrar/unrar-3.7.4-1.el5.rf.x86_64.rpm

To extract rar file, format:
unrar e /path/to/file.rar

Eg.:
unrar e /home/me/somefile.rar