i have been using include files in templates to share common code, which on reflection I ought to have maybe implemented as custom theme functions, anyway...
the issue is that to make the include statement work correctly you need the absolute path to the folder, you could create a full url but accessing files in this way is normally blocked in server configurations, and you could change the php.ini file but sometimes there are restrictions on that, so after few hours of trial and error and searching forums to no avail, I have this solution that works
in the settings.php I have added the following code to setup a value in "variables":
$conf = array('themename_fullthemepath' => '/wamp/www/examplesite/sites/all/themes/_custom/themename' );
and in page.tbl.php I have added the following code
$theme_dir = variable_get("themename_fullthemepath", "novalue_defined_in_settings.php");
$include_dir = $theme_dir .'/includes';
include "$include_dir/header.inc"
it allows me to test on my PC and also in hosted environment once i have the settings file correctly configured for the two evironments
