I put the files used at this site for the Theme-o-rama module in the "Etc." file gallery (tiki-list_file_gallery.php?galleryId=12). You can use these as a model if you like. Just change the theme names, file names and so on to suit your site. The php file goes in the /modules directory and the tpl file goes in /templates/modules. After you upload the files, the new module should show up in the list on your Admin Modules page.