When developing my website I called all the includes in my php files by calling one single file called includes.
The code of this file looked somethig like this: (I
First off: I'd drop the DS, it's BS (ehe). Windows support both C:/wamp/www and C:\wamp\www :-) Even C:\wamp\www/project is fine.
If includes.php is located in, say lib/includes.php (relative to your project root), then do this:
define('SITE_ROOT', realpath('../'));
That will dynamically set SITE_ROOT.