Addition to "Date Based Category Archives for Wordpress"

<?php
$anho_actual = (get_query_var('year')) ? get_query_var('year') : 0;
$mes_actual = (get_query_var('monthnum')) ? get_query_var('monthnum') : 0;

if ($anho_actual == 0 || $mes_actual == 0)
{
    $anho_actual = date("Y");
    $mes_actual = date("m");

    global $query_string;

    $query_string .= "&year=".$anho_actual."&monthnum=".$mes_actual;
    query_posts($query_string);

}

$anho_previo = $anho_actual;
$anho_proximo = $anho_actual;

$categoria = get_cat_ID(  get_query_var('category_name') );

$category_link = get_category_link( $categoria );

$mes_previo = $mes_actual - 1;

if ($mes_previo == 0)
{
    $mes_previo = 12;
    $anho_previo = $anho_actual - 1;
}

$mes_proximo = $mes_actual + 1;

if ($mes_proximo == 13)
{
    $mes_proximo = 1;
    $anho_proximo = $anho_actual + 1;
}

$dummy_date = strtotime($anho_actual."-".$mes_actual."-1");
?>

<div id="nav">

<div class="prev"><h1><a href="<?=$category_link;?><?=$anho_previo;?>/<?=$mes_previo;?>">&lt;</a></h1></div>

<div class="mes"><h1><?=strftime("%b", $dummy_date);?><span><?=strftime("%Y", $dummy_date);?></span></h1></div>

<div class="next"><h1><a href="<?=$category_link;?><?=$anho_proximo;?>/<?=$mes_proximo;?>">&gt;</a></h1>
</div>