Código PHP:
<form action="" method="post" name="frmFiltro" id="frmFiltro">
<table width="228" border="0" align="center">
<tr>
<td width="74">Periodo:</td>
<td width="96"><label>
<select name="select" id="select">
<?php
do {
?>
<option value="<?php echo $row_Periodo['idPeriodo']?>"><?php echo $row_Periodo['Descripcion']?></option>
<?php
} while ($row_Periodo = mysql_fetch_assoc($Periodo));
$rows = mysql_num_rows($Periodo);
if($rows > 0) {
mysql_data_seek($Periodo, 0);
$row_Periodo = mysql_fetch_assoc($Periodo);
}
?>
</select>
</label></td>
</tr>
<tr>
<td>Categoria:</td>
<td><label>
<select name="select2" id="select2">
<option value="Primera Division">Primera Division</option>
<option value="Division Infantil">Division Infantil</option>
<option value="Pre-cadete">Pre-cadete</option>
<option value="Cadete">Cadete</option>
<option value="Sub 13">Sub 13</option>
<option value="Sub 15">Sub 15</option>
<option value="Sub 17">Sub 17</option>
<option value="Sub 19">Sub 19</option>
</select>
</label></td>
</tr>
<tr>
<td> </td>
<th>
<label>
<input name="btn" id="btn" type="button" onClick="location.href = 'registrado.php?seccion=filtrados&Periodo=<?php echo $row_Periodo['idPeriodo']; ?>'" value="Buscar">
</label>
</th>
</tr>
</table>
</form>