How To To Install Flex In Linux

mine works fine.. check to make sure you are sending the command as sudo or root

[root@testvirtual ~]# yum install flex
Loaded plugins: fastestmirror
Determining fastest mirrors
 * addons: mirrors.versaweb.com
 * base: centos.mirrors.tds.net
 * extras: mirror.unl.edu
 * updates: mirror.chpc.utah.edu
addons                                                                                       |  951 B     00:00
addons/primary                                                                               |  202 B     00:00
base                                                                                         | 2.1 kB     00:00
base/primary_db                                                                              | 1.6 MB     00:10
extras                                                                                       | 2.1 kB     00:00
extras/primary_db                                                                            | 181 kB     00:01
updates                                                                                      | 1.9 kB     00:00
updates/primary_db                                                                           | 915 kB     00:07
Setting up Install Process
Package flex-2.5.4a-41.fc6.i386 already installed and latest version
Nothing to do

[root - at - localhost ~]# yum install flex
Traceback (most recent call last):
File "/usr/bin/yum", line 22, in <module>
import yummain
File "/usr/share/yum/yummain.p line 22, in <module>
import clientStuff
File "/usr/share/yum/clientStu line 18, in <module>
import rpm
ImportError: No module named rpm

i wanted to know how to install it on rhel-4, becoz its yum is not working. can you suggest any link for step by step process