Código PHP:
for ($indece=0; $indece < count ($_POST['claves']) and ($_POST['volumennuevo']); $indece++){
echo "<tr><td><font size = \"1\">".$_POST['claves'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['descconcepto'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['unidad'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['pu'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['cantidad'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['volumennuevo'][$indece]."</td>";
echo "<td><font size = \"1\">".$_POST['importenuevo'][$indece]."<td>";
while($rows = mysql_fetch_assoc($datosestimacion)){
echo "<td><font size = \"1\">$rows[volumenac]</font></td>
<td><font size = \"1\">$rows[importeac]</font></td>";
$volumenac = $rows[volumenac]+$_POST['volumennuevo'][$indece];
echo "<td><font size = \"1\">$volumenac</fon></td>";
$importeac = $rows[importeac]+$_POST['importenuevo'][$indece];
echo "<td><font size = \"1\">$importeac</font></td></tr>";
}
}