Aspetta....lo riposto bene:

<?php
require_once('config.php');
$art_per_pag = 8;
$start=0;
$stop=$art_per_pag;
$sql = "SELECT * FROM pagine ORDER by 'id' ";
if (!isset($_GET[pag]) or ($_GET[pag]==1)){
$sql .= " LIMIT $start, $stop";
}else{
$stop = $art_per_pag * $_GET[pag];
$start = $stop - $art_per_pag + 0;
$sql .= " LIMIT $start, $stop";
}
$query = mysql_query($sql);
while($row = mysql_fetch_array($query)) {
$html = "<div id='box'>";
$html .= "<div id='title'>";
$html .="<div id='testo'>";
$html .= "$row[titolo]";
$html .= "</div>";
$html .="<div id='prezzo'>";
$numero=$row[prezzo];
$numm=number_format( $numero , 2 , "," , "." );
$html .= "€ $numm";
$html .= "</div>";
$html .= "</div>";
$html .= "<div id='img'>";
$sql_img = "SELECT * FROM immagini WHERE paginaid=$row[id] AND copertina=1 LIMIT 1 ";
$query_img = mysql_query($sql_img);
$row_img = mysql_fetch_array($query_img);
$html .= "[img]foto/$row_img[immagine][/img]";
$html .= "</div>";
$html .= "<div id='art'>";
$testo = "$row[testo]";
$preview = substr($testo,0 , 310);
$html .= "$preview..." ."
";
$html .= "<div id='dettagli'>";
$html .= "dettagli";
$html .= "</div>";
$html .= "</div>";
$html .= "</div>";
echo $html;
}
?>
<div style="position:relative;top:10px;padding:0;">
<?php
$num_page = (!isset($_GET[pag]) || empty($_GET[pag]) ? 1 : $_GET[pag]);
$perpage = 8;

$num_articoli_totali = 80;
$next = $prev = false;
$pagine_tot=ceil($num_articoli_totali/$perpage);


$link="";
if(($pagina==1)&&($num_articoli_totali<=8)) <--ma qui non dovrebbe essere $num_pag invece che $pagina?
{
$link.="";
}
else{
if(($num_page!=1)&&($num_page<=$pagine_tot))
{
$pag=$num_page-1;
$link.="<a style=\"color:#BC040E;text-decoration:none\" href=articoli.php?pag=$pag>Prev</a>";
}
if(($num_page>0)&&($num_page<$this->$pagine_tot))
{
$pag=$num_page+1;
$link.="<a style=\"color:#BC040E;text-decoration:none\" href=articoli.php?pag=$pag>Next</a>";
}
}
echo $link;

?>
</div>