$query_rs_npc = "SELECT npc.npcid
FROM npc
LEFT JOIN
npc_2_loot
ON npc_2_loot.npcid = npc.npcid
WHERE npc_2_loot.npcid IS NULL
ORDER BY npc.npcid ASC";

$query_rs_npc = "SELECT npc.npcid
FROM npc
WHERE npc.npcid NOT IN (SELECT DISTINCT npc_2_loot.npcid FROM npc_2_loot)";
$row_npc = mysql_query($query_rs_npc) or die(mysql_error());
$row_rs_npc = mysql_fetch_assoc($row_npc);
$rs_npc = mysql_num_rows($row_npc);
echo $rs_npc;

You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'IN (SELECT DISTINCT npc_2_loot.npcid FROM npc_2_loot)' at line

$sql = "SELECT s.grouptitle, l.groupname
      FROM sgroup s INNER JOIN loot_drop l
      ON s.sgid = l.sgid";
$res = mysql_query($sql) or die(mysql_error());
#
# store names in array for each title
# it makes the table columns code a lot simpler
#
$array = array();
while (list($t, $n) = mysql_fetch_row($res)) {
      $array[$t][] = $n;
}

#
# now output the array into a 4 column table
#

define ("NUMCOLS",4);

$count = 0;

echo "<table border='0' cellpadding='4' cellspacing='2' width='500'>\n";
foreach ($array as $title => $names) {
    # new row every NUMCOLS cells
    if ($count % NUMCOLS == 0) echo "<TR valign='top'>\n";
    echo "  <TD width='25%'>\n";
    echo "  <div style='border: solid 1pt silver'>$title</div>\n";

    # now names for the title
    foreach ($names as $n) {
         echo "    $n<br/>\n";
    }

    echo "    <br/>\n  </TD>\n";
    $count++;

    # end row if we've just done NUMCOLs cells
    if ($count % NUMCOLS == 0) echo "</TR>\n";
}

if ($count % NUMCOLS != 0) {
   # end row if not already ended
   while ($count++ % NUMCOLS) echo "<td>&nbsp;</td>";
   echo "</TR>\n";
}

echo "</table>\n";