$currentPost->showPost($isadmin, $forumdata);
Look in newbb/class for the file in which the method showPost() is defined, to figure out what it does. Maybe it assigns the smarty variable "topic_posts".
$xoopsTpl->append('topic_posts', ...);
Warning: include_once(/Frameworks/art/functions.ini.php) [function.include-once]: failed to open stream: No such file or directory in file /modules/newbb/xoops_version.php line 57