in global.php you'll see the code...
Code:
// templates to be included in every single page...
$globaltemplates = array_merge($globaltemplates, array(
// the really important ones
'header',
'footer',
'headinclude',
'phpinclude_start',
'phpinclude_end',
........
add 'your_template', in that list replacing your_template with your custom template.
so that it looks something like
Code:
// templates to be included in every single page...
$globaltemplates = array_merge($globaltemplates, array(
// the really important ones
'header',
'your_template',
'footer',
'headinclude',
'phpinclude_start',
'phpinclude_end',
....
g/l