Drupal comes with many handy modules, not the least of which are the Adsense and Adsense Injector modules - which let you control the look, feel, and placement of your Adsense ads within your Drupal pages. The problem? The Adsense injector, while having the right intentions, isn't quite to the level where it will allow you to "inject" ads into the middle of your content. For the more technically inclined - in your theme's node.tpl.php file, the print $content statement prints the actual body of your content.