es relativamente facil
como implementarlo :
1 copiar el siguiente codigo en el archivo template.php del tema de preferencia al final
function node_sibling($dir = 'next', $node, $next_node_text=NULL, $prepend_text=NULL, $append_text=NULL, $tid = FALSE){
if($tid){
$query = 'SELECT n.nid, n.title FROM {node} n INNER JOIN {term_node} tn ON n.nid=tn.nid WHERE '
. 'n.nid ' . ($dir == 'previous' ? '<' : '>') . ' :nid AND n.type = :type AND n.status=1 '
. 'AND tn.tid = :tid ORDER BY n.nid ' . ($dir == 'previous' ? 'DESC' : 'ASC');
//use fetchObject to fetch a single row
$row = db_query($query, array(':nid' => $node->nid, ':type' => $node->type, ':tid' => $tid))->fetchObject();
}else{
$query = 'SELECT n.nid, n.title FROM {node} n WHERE '
. 'n.nid ' . ($dir == 'previous' ? '<' : '>') . ' :nid AND n.type = :type AND n.status=1 '
. 'ORDER BY n.nid ' . ($dir == 'previous' ? 'DESC' : 'ASC');
//use fetchObject to fetch a single row
$row = db_query($query, array(':nid' => $node->nid, ':type' => $node->type))->fetchObject();
}
if($row) {
$text = $next_node_text ? $next_node_text : $row->title;
return $prepend_text . l($text, 'node/'.$row->nid, array('rel' => $dir)) . $append_text;
} else {
return FALSE;
}
}
2. este codigo lo pegan en el el archivo tpl
si no crearon un tpl personalizado entonces deberian pegarlo en node.tpl.php
<?php
$next = node_sibling('next',$node,NULL,NULL,NULL,FALSE);
$previous = node_sibling('previous',$node,NULL,NULL,NULL,FALSE);
print $previous.'||'.$next;
?>
