As far as I know, (and I could be wrong) you have to have Joomla installed in order to use RocketLauncher - please correct me if I am wrong guys.
Actually, RocketLauncher contains a full Joomla install in addition to the demo content and template. So, by running the RocketLauncher, you will be both installing a new copy of Joomla 1.0.13 (which is necessary as the demo content is inserted during the joomla install process) as well as the demo content and template. RocketLauncher won't work with an existing Joomla install.
Just upload the contents of the Joomla_RT_Templatename folder inside the zip, to your root directory on the server (same as you would with a normal Joomla install package) then point your browser to the root to begin the installation.