Did you actually check the contents of 'index.php' in /opt/lampp/htdocs on the new server to make sure it was written out correctly? As in owner and permissions checking as well? (should be nobody:root, 644 probably). If the ownership was root:root it probably would not work right. (just a recollection)
I'm not at work right now (on site) so I can't easily dig through my lampp box.