How do I install automake and autoconf on RedHat Enterprise 5?

These should be installable via yum and the base RHEL repositories. Have you tried querying if they are already installed but not in your path? Also, have you successfully installed anything via yum?

To check what package you need to install:

[user@server]# yum whatprovides autoconf automake
Loaded plugins: rhnplugin, security
autoconf-2.59-12.noarch : A GNU tool for automatically configuring source code.
Repo        : rhel-x86_64-server-5
Matched from:

automake-1.9.6-2.1.noarch : A GNU tool for automatically creating Makefiles.
Repo        : rhel-x86_64-server-5
Matched from:

These RHEL repositories can be installed using yum utility. A good feature is to enable another repository from your own DVD installation disc. A complete step-by-step description can be found here. http://saifulaziz.com/2014/02/26/howto-install-redhat-package-with-yum-command-without-rhn/

Once you did it, you can install automake, or autoconf from this "new" repository. In other words, you can bypass the warning message of "This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register."