The HomepageGrid extension gives you numerous options via it's config panel. By visiting System -> Configuration -> RT RokMage Modules you have access to all the settings available. These will allow you to set your store up as you see fit.
We also supply an "extensions settings" file, available in the theme download pages, that can be used to preconfigure the extensions to match your chosen theme. This is included by default in all theme RocketLaunchers.