According to the page you linked, it points to http://s3tools.org/repositories. According to the official Amazon S3 Tools site:
S3cmd requires Python 2.6 (or newer)
and
Note: the [LINUX repositories at http://s3tools.org/repositories] are
NOT up to date. Download the latest version of S3cmd from SourceForge
or GitHub above or get the s3cmd package from your Linux
distribution's own repositories.
If yum install s3cmd with your default repos (or possibly EPEL) does not work for some reason, then you can install from SourceForge. The latest release is 1.6.1, so download that from here. Once you have it downloaded, do the following:
$ tar -xzf s3cmd-1.6.1.tar.gz
$ cd s3cmd-1.6.1
$ sudo python setup.py install
This will extract the .tar.gz file, and navigate into the extracted folder, and run the s3cmd install script.
Note, that according to the INSTALL file, you need the Python "distutils" module:
You will however need Python "distutils" module for this to work. It
is often part of the core python package (e.g. in OpenSuse Python 2.5
package) or it can be installed using your package manager, e.g. in
Debian use
apt-get install python-setuptools
Again, consult your distribution documentation on how to
find out the actual package name and how to install it then.