1. Unzip and copy the infinite folder to the wordpress plugin folder
   (usually ./wp-content/plugins/).
2. Go to the folder of your current theme and open the index.php file
3. Copy everything between "while (have_posts()) : the_post();" and
   "endwhile;" to the ./wp-content/plugins/infinite/post.tpl.php file.
   That's the template for the post which is fetched via AJAX.
4. Go to the plugins admin page and activate the Infinite Scrolling Plugin.