te muestro el codigo completo
Cita: <script language='JavaScript'>
var cont=0;
function addRow(t)
{
cont++;
var indiceFila=1;
myNewRow = document.getElementById('tabla').insertRow(-1);
myNewRow.id=indiceFila;
myNewCell=myNewRow.insertCell(-1);alert(cont);
myNewCell.innerHTML='<td><input type="text" size="15" name="lote'+cont+'" /></td>';
myNewCell=myNewRow.insertCell(-1);
myNewCell.innerHTML='<td><input type="text" size="15" name="serial'+cont+'" /></td>';
myNewCell=myNewRow.insertCell(-1);
myNewCell.innerHTML='<input type="text" size="10" name="mfd'+cont+'"/>';
for(var U=0; U<t; U++){
myNewCell=myNewRow.insertCell(-1);
myNewCell.innerHTML='<input type="text" size="8" name="cantdef'+cont+'"/>';
}
indiceFila++;
}
function borrar() {
var table = document.getElementById('tabla');
if(table.rows.length > 3)
{
table.deleteRow(table.rows.length-1);
cont--;
}
}
</script>
<table border="1" id="tabla" cellspacing="1" align="center">
<tr align="center">
<td colspan="3"><b>Detalles</b></td>
<td colspan="<?=$j;?>"><b>Cantidad de Defectos</b></td>
</tr>
<tr align="center">
<td>Lote</td>
<td>Serial</td>
<td>MFD</td>
<?php
$sql_def="SELECT * FROM def,pie
WHERE pie.icve_pieza=def.icve_pieza
and pie.icve_pie='$icve_pie'";
$result_def=mysql_query($sql_def);
$result_def2=mysql_query($sql_def);
$num_def=mysql_num_rows($result_def2);
//echo "<p>Num_def: $num_def<p>";
echo "<input type='hidden' name='num_def_php' value='$num_def'>";
$j=1;
while($row_d = mysql_fetch_array($result_def))
{
$icve_defecto = $row_d['icve_defecto'];
$cdesc_def = $row_d['cdesc_defecto'];
//echo "<span>$j. <input type='text' name='def$j' size='5' value='0'> <b>$cdesc_def</b> <br /> </span>";
echo "<input type='hidden' name='cdesc_def$j' value='$cdesc_def'>";
?><td><?=$cdesc_def;?></td><?
$j++;
}?>
</tr>
<tr>
<td><input type="text" size="15" name="lote[]"/></td>
<td><input type="text" size="15" name="serial[]"/></td>
<td><input type="text" size="10" name="mfd[]"/></td>
<? $sql_def="SELECT * FROM def,pie
WHERE pie.icve_pieza=def.icve_pieza
and pie.icve_pie='$icve_pie'";
$result_def=mysql_query($sql_def);
$result_def2=mysql_query($sql_def);
$num_def=mysql_num_rows($result_def2);
// echo "<input type='hidden' name='num_def_php' value='$num_def'>";
$t=0;
while($row_d = mysql_fetch_array($result_def))
{
$icve_defecto = $row_d['icve_defecto'];
$cdesc_def = $row_d['cdesc_defecto'];
//echo "<span>$j. <input type='text' name='def$j' size='5' value='0'> <b>$cdesc_def</b> <br /> </span>";
//echo "<input type='hidden' name='cdesc_def$j' value='$cdesc_def'>";
?><td><input type="text" size="8" name="cantdef[]"/></td>
<? $t++; } ?>
<input type="hidden" name="var_cont">
//mando t para que me genere textbox de a la consulta
<td valign="top"><input type="button" name="b1" value="[+]" onClick="addRow('<?=$t;?>')"></td>
<td valign="top"><input type="button" name="b2" value="[-]" onClick="borrar()"></td>
</tr>
</table>