Well, first off, if you want to display any custom template you'll need to parse it. Add the following code to your PHPINCLUDE_START template
PHP Code:
eval('$TEMPLATENAME = "' . fetch_template('TEMPLATENAME') . '";');
Now as to the rest of you're question, I'm not sure I fully understand. Are you wanting to open a page which is defined in that template?? If so, then do this..
The link to the template in you're header should read
HTML Code:
<a href="index.php?do=PAGE">LINK ME</a>
Where PAGE is the basic name of your page. Then put this in the PHPINCLUDE_START template
PHP Code:
if ($_REQUEST['do'] == 'PAGE' AND THIS_SCRIPT=='index')
{
eval('print_output("' . fetch_template('TEMPLATENAME') . '");');
}