So for those of you who are having trouble as well using XHTML with PHP, I present to you a short tutorial to make sure they work correctly together.
The problem is the very first line in a XHTML page.
<?xml version="1.0" encoding="iso-8859-1"?>Using that in conjunction with your php includes, or other php code causes the page to error because PHP thinks that the <?xml... tag is PHP as well.
To fix:
Open your php.ini file and look for:
short_open_tag = Onand change it to:
short_open_tag = Off
Save and close it. Now in order to use php code; you must start with <?php... instead of the short tag <?...
However you should now be able to use PHP and XHTML together flawlessly.