forum display

I have developed a forum at:
http://www.acpchnqld.org.au/forum/forum.php

The initial list does not have a method for displaying the previous posts at
this stage. I would like a row at the bottom of the list to provide
relevant links for 'older messages' and/or 'newer messages'.

The code I think may provide this is;
if (!$result){
$num_msgs = mysql_numrows($result);
$prev = $next - $rpp;
$next += $rpp;
echo"<tr><td colspan='3' bgcolor = '#EEF5FE' align = right>";
if($next <= $num_msgs)echo"<a href=\"forum.php?next=$next\">Older
Messages</a>";
if(($next <= $num_msgs) && ($prev >= 0))echo"&nbsp;&nbsp;|&nbsp;&nbsp;";
if($prev >= 0)echo"<a href=\"forum.php?next=$prev\">Newer Messages</a>";
echo"</td></tr>";
}

However I've tried to place this code within the structure of the list and
can only make it appear at the top of the list. Also the parameters being
passed in the URL (eg next=20) don't have any effect on the display,
effectively being ignored. I'm unsure why this is.

The full code for this file is below. Appreciate any suggestions
Thanks
David

FULL CODE:
<?
// functions for loading, contructing and
// displaying the tree

class treenode
{
// each node in the tree has member variables containing
// all the data for a post except the body of the message
var $m_postid;
var $m_title;
var $m_poster;
var $m_posted;
var $m_children;
var $m_childlist;
var $m_depth;

function treenode($postid, $title, $poster, $posted, $children,
$expand, $depth, $expanded, $sublist)
{
// the constructor sets up the member variables, but more
// importantly recursively creates lower parts of the tree
$this->m_postid = $postid;
$this->m_title = $title;
$this->m_poster = $poster;
$this->m_posted = $posted;
$this->m_children =$children;
$this->m_childlist = array();
$this->m_depth = $depth;

// we only care what is below this node if it
// has children and is marked to be expanded
// sublists are always expanded
if(($sublist||$expand) && $children)
{
$conn = db_connect();

if(!$next){ $next=0;
}

$rpp = 20;//results per page
$query = "select * from header where parent = $postid order by posted
desc limit $next, $rpp";
$result = mysql_query($query);

for ($count=0; $row = @mysql_fetch_array($result); $count++)
{
if($sublist||$expanded[ $row['postid'] ] == true)
$expand = true;
else
$expand = false;
$this->m_childlist[$count]= new
treenode($row['postid'],$row['title'],
$row['poster'],$row['posted'],
$row['children'], $expand,
$depth+1, $expanded, $sublist);
}
}
}

function display($row, $sublist = false)
{
// as this is an object, it is responsible for displaying itself
// $row tells us what row of the display we are up to
// so we know what color it should be
// $sublist tells us whether we are on the main page
// or the message page. Message pages should have
// $sublist = true.
// On a sublist, all messages are expanded and there are
// no "+" or "-" symbols.
// if this is the empty root node skip displaying
if($this->m_depth>-1)
{
//color alternate rows
echo "<tr><td bgcolor = ";
if ($row%2)
echo "'#EEF5FE'>";
else
echo "'#ffffff'>";

// indent replies to the depth of nesting
for($i = 0; $i<$this->m_depth; $i++)
{
echo "<img src = 'images/spacer.gif' height = 12
width = 10 alt = '' valign = bottom>";
}

// display + or - or a spacer
if ( !$sublist && $this->m_children && sizeof($this->m_childlist))
// we're on the main page, have some children, and they're expanded
{
// we are expanded - offer button to collapse
echo "<a href = 'forum.php?collapse=".
$this->m_postid."#$this->m_postid'
><img src = 'images/minus.gif' valign = bottom
height = 9 width = 9 alt = 'Collapse Thread' border = 0></a>";
}
else if(!$sublist && $this->m_children)
{
// we are collapsed - offer button to expand
echo "<a href = 'forum.php?expand=".
$this->m_postid."#$this->m_postid'><img src = 'images/plus.gif'
height = 9 width = 9 alt = 'Expand Thread' border = 0></a>";
}
else
{
// we have no children, or are in a sublist, do not give button
echo "<img src = 'images/spacer.gif' height = 9 width = 9
alt = ''valign = bottom>";
}

echo " <a name = $this->m_postid >
<a href = 'view_post.php?postid=$this->m_postid'>$this->m_title </td>
<td class='forumtext' bgcolor = ";
if ($row%2) {
echo "'#EEF5FE'>";
}
else{
echo "'#ffffff'>";
}

echo "$this->m_poster</td><td class='forumtext' bgcolor = ";
if ($row%2) {
echo "'#EEF5FE'>";
}
else{
echo "'#ffffff'>";
}
echo "".reformat_date($this->m_posted)."</a>";
echo "</td></tr>";

// increment row counter to alternate colors
$row++;
}
// call display on each of this node's children
// note a node will only have children in its list if expanded
$num_children = sizeof($this->m_childlist);
for($i = 0; $i<$num_children; $i++)
{
$row = $this->m_childlist[$i]->display($row, $sublist);
}
return $row;
}
};
?>