The include path is set against the server configuration (PHP.ini) but the include path you specify is relative to that path so in your case the include path is (actual path in windows):
C:\xampp\php\PEAR\initcontrols\header_myworks.php
providing the path you pasted in the subject is correct. Make sure your file is located there.
For more info you can get and set the include path programmatically.