<?php
$taxonomy = 'categories';
$orderby = 'name';
$show_count = 0; // 1 for yes, 0 for no
$pad_counts = 0; // 1 for yes, 0 for no
$hierarchical = 1; // 1 for yes, 0 for no
$title = 'Categories';
$empty = 0;
$args = array(
'taxonomy' => $taxonomy,
'orderby' => $orderby,
'show_count' => $show_count,
'pad_counts' => $pad_counts,
'hierarchical' => $hierarchical,
'title_li' => $title,
'hide_empty' => $empty,
);
$cats = explode("<br />",wp_list_categories( $args ));
$cat_n = count($cats) - 1;
for ($i=0;$i<$cat_n;$i++):
if ($i<$cat_n/2):
$cat_left = $cat_left.'<li>'.$cats[$i].'</li>';
elseif ($i>=$cat_n/2):
$cat_right = $cat_right.'<li>'.$cats[$i].'</li>';
endif;
endfor;
?>
<ul class="left">
<?php echo $cat_left;?>
</ul>
<ul class="right">
<?php echo $cat_right;?>
</ul>