I would like to set up a gallery of all my themes and when the user clicks on the item it would go to a pre-setup Drupal instance and it would set that instance with the theme they clicked so they can see the theme in action. I know how to create a photo gallery but i want to have the images when click go to a sub site that is preset to change the default theme to the one passed in the link so that the user can see the live theme. I would like to have one sub site and have that sub site have all the themes installed and simple change the enabled theme based on the request. The user clicking on the images in the gallery will not be logged in. I don't want to make a different site for each theme. That would be to much unneeded work and to many databases that do not need to be. using modules would be the best over making custom code for this.
The ThemeKey module would help you to achieve this.
ThemeKey allows you to define simple or sophisticated theme-switching rules which allow automatic selection of a theme depending on current path, taxonomy terms, language, node-type, and many, many other properties. It can also be easily extended to support additional properties exposed by other modules.