This tip might help when your php scripts with include files work on your server but give variable undefined errors inside XAMPP.
I'm using XAMPP v 1.7.7 and in the php.ini file changed the error reporting from:-
error_reporting = E_ALL | E_STRICT
error_reporting = E_ALL & ~E_NOTICE
I know very little about all this but it solved my problem and now my scripts work the same inside XAMPP as they do on my Linux hosted server.