The latest version of RPM is always in latest/.

rpm-1.x/		old versions of RPM 1.x
rpm-2.0.x/              old versions of RPM 2.0.x
rpm-2.1.x/              old versions of RPM 2.1.x
rpm-2.2.x/              old versions of RPM 2.2.x
rpm-2.3.x/              old versions of RPM 2.3.x

The .tar.gz files are pre-built binaries for RPM.  To extract them:

tar xvzf file.tar.gz

As of RPM 2.4, nearly any version of cpio will work fine with RPM. When
you first install RPM, you may need to "mkdir /var/lib/rpm" before installing
your first package.

NOTE: If you use RPM 2.1.x or later on a Red Hat 3.0.3 system or earlier,
      you *will* get unresolved dependencies. To work around this,
      install these packages with the --nodeps option. If you don't
      know why this is happening or what this means, upgrade to Red Hat
      4.x and don't worry about it.

NOTE: If you are upgrading to RPM 2.2 from RPM 2.0.x, you must first upgrade
      to RPM 2.1.2, which can be found in the rpm-2.1.x directory.

NOTE: If you are upgrading from RPM 1.x, you must first upgrade to RPM
      2.0.0 by following the instructions in the README file located
      in the rpm-2.0.x/update directory.