The Knacks

<MTArchiveList archive_type="Category">
<?php $category_archives["<$MTArchiveTitle$>"] = "<$MTArchiveLink$>"; ?>
</MTArchiveList>
<?php
$values = count($category_archives);
if ((floor($values / 2) * 2) == $values) {
    $row_count = $values / 2;
}
else {
    $row_count = floor($values / 2) + 1;
}
?>
<table class="sidetable">
<?php $values = count($category_archives);
if ((floor($values / 2) * 2) == $values) {
    $row_count = $values / 2;
}
else {
    $row_count = floor($values / 2) + 1;
}
?>
<table class="sidetable">
<?php
$i = 0;
foreach ($category_archives as $title => $link) {
    $titles[$i] = $title;
    $links[$i] = $link;
    $i++;
}

for ($i = 0; $i < $row_count; $i++) {
    echo "<tr class=\"sidetable\">\n";
        $second = $i + $row_count;
        echo "<td class=\"lsidetable\"><a href=\"$links[$i]\" title=\"$titles[$i]\">$titles[$i]</a></td>\n";
        echo "<td class=\"rsidetable\"><a href=\"$links[$second]\" title=\"$titles[$second]\">$titles[$second]</a></td>\n";
    echo "</tr>\n";
}
?>
</table>
</div>

The associated style sheet excerpt is here:

table.sidetable {
    border-collapse: collapse;
    table-layout: auto;
    border: 0;
    text-align: center;
}

tr.sidetable {
}

td.lsidetable {
    border-right: 2px ridge;
    border-left: 0;
    padding-left: 0;
    padding-right: 2em;
    text-align: right;
    padding-left: 2em;
}

td.rsidetable {
    border-right: 0;
    border-left: 2px ridge;
    padding-left: 2em;
    padding-right: 0;
    text-align: left;
}