Difference between theme preprocessor & processor function?
For the template

If the page is "/my-node", the page template will be "page--my-node.tpl.php".

For the Prepocess

But you cannot using it "themename_preprocess_my_node(&amp;$vars)" because my-node isn't a hook ! You can find differents hooks with this page http://api.drupal.org/api/drupal and with the search box,  type 'theme_'. You can see the differents hooks for the preprocess