Page id based on file path?
You need to edit your page.tpl.php file, and add this where you have the &lt;body&gt; tag. 

&lt;body class="&lt;?php
   print arg(0, request_path());
?&gt;


This will print the first part of $_SERVER['REQUEST_URI'] delimited by a slash. 
arg() and request_path() are Drupal functions.