Originally posted by da_silvy
does it not work just

include('header.php');

it's in the same directory as the file which is including it isn't it?
header.php is in the root directory. Any php files in the root directly using include() work just fine. The problem comes up when I'm trying to include it from a php file in a subdirectory. That's why you see so many $DOCUMENT_ROOTs floating around in this thread