Continuación del código.
Código PHP:
<body bgcolor="#F5F5F5" topmargin="10">
<table width="836" cellpadding="0" cellspacing="0" border="0">
<tr>
<td colspan="8">
<iframe name="navigation" src="cabecera.html" frameborder="0" width="836" scrolling="no" height="118"></iframe>
</td>
</tr>
<tr>
<td colspan="8" width="836" height="8" bgcolor="#FFFFFF"></td>
</tr>
<tr>
<td colspan="8" width="836" height="22" bgcolor="#F5F5F5"></td>
</tr>
<tr>
<td colspan="8" height="29" bgcolor="#F5F5F5">
<img src="imagenes/gestionar.gif" width="183" height="29" />
</td>
</tr>
<tr>
<td colspan="8" width="836" height="22" bgcolor="#F5F5F5">
</tr>
<tr>
<td colspan="8" width="836" height="8" bgcolor="#FFFFFF"></td>
</tr>
<tr bgcolor="#FFFFFF">
<td colspan="2" width="209" align="right" style="padding-right:5px">Categoría del producto:</td>
<td colspan="2" width="209" align="left">
<select name="categoria" id="categoria" onChange="crearSubSelect()" onClick="crearSubSelect()" onKeyPress="crearSubSelect()">
<option value="accesorios_viaje">Accesorios de viaje</option>
<option value="casa_hogar">Casa y hogar</option>
<option value="cuidado_personal">Cuidado personal</option>
<option value="escritura">Escritura</option>
<option value="herramientas_linternas">Herramientas y linternas</option>
<option value="ocio">Ocio</option>
<option value="oficina">Oficina</option>
<option value="regalos">Regalos</option>
<option value="sonido_imagen">Sonido e imagen</option>
<option value="tiempo">Tiempo</option>
</select>
</td>
<td colspan="2" width="209" align="right" style="padding-right:5px">Subcategoría del producto:</td>
<td colspan="2" width="209" align="left" id="subCategoria"></td>
</tr>
<tr bgcolor="#FFFFFF">
<td colspan="8" width="836" height="16"></td>
</tr>
<tr align="right" bgcolor="#FFFFFF">
<form name="boton" method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<td colspan="2" width="209"><input name="insertar" type="button" id="insertar" value="Insertar" /></td>
<td colspan="2" width="209"><input name="modificar" type="button" id="modificar" value="Modificar" /></td>
<td colspan="2" width="209"><input name="borrar" type="button" id="borrar" value="Borrar" /></td>
</form>
<td colspan="2" width="209"></td>
</tr>
<tr bgcolor="#FFFFFF">
<td colspan="8" width="836" height="16"></td>
</tr>
<?php
if ($_POST['insertar'])
{
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td colspan=2 width=209>Referencia:</td>";
echo "<td colspan=2 width=209><input name=\"referencia\" type=\"text\" id=\"referencia\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td colspan=2 width=209>Código de marcaje:</td>";
echo "<td colspan=2 width=209><input name=\"codigo_marcaje\" type=\"text\" id=\"codigo_marcaje\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
echo "<tr bgcolor=\"#FFFFFF\"><td colspan=\"8\" width=\"836\" height=\"8\"></td></tr>";
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td colspan=2 width=209>Descripción:</td>";
echo "<td colspan=2 width=209><input name=\"descripcion\" type=\"text\" id=\"descripcion\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td colspan=2 width=209>Medida de marcaje:</td>";
echo "<td colspan=2 width=209><input name=\"medida_marcaje\" type=\"text\" id=\"medida_marcaje\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
echo "<tr bgcolor=\"#FFFFFF\"><td colspan=\"8\" width=\"836\" height=\"8\"></td></tr>";
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td colspan=2 width=209>Colores:</td>";
echo "<td colspan=2 width=209><input name=\"colores\" type=\"text\" id=\"colores\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td colspan=2 width=209>Colores máximos de marcaje:</td>";
echo "<td colspan=2 width=209><input name=\"colores_maximos\" type=\"text\" id=\"colores_maximos\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
echo "<tr bgcolor=\"#FFFFFF\"><td colspan=\"8\" width=\"836\" height=\"8\"></td></tr>";
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td colspan=2 width=209>Precio según las unidades:</td>";
echo "<td colspan=2 width=209></td>";
echo "<td colspan=2 width=209>Incremento:</td>";
echo "<td colspan=2 width=209><input name=\"incremento\" type=\"text\" id=\"incremento\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
echo "<tr bgcolor=\"#FFFFFF\"><td colspan=\"8\" width=\"836\" height=\"8\"></td></tr>";
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td>25</td>";
echo "<td><input name=\"25\" type=\"text\" id=\"25\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>100</td>";
echo "<td><input name=\"100\" type=\"text\" id=\"100\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>500</td>";
echo "<td><input name=\"500\" type=\"text\" id=\"500\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>5000</td>";
echo "<td><input name=\"5000\" type=\"text\" id=\"5000\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
echo "<tr bgcolor=\"#FFFFFF\"><td colspan=\"8\" width=\"836\" height=\"8\"></td></tr>";
echo "<tr bgcolor=\"#FFFFFF\">";
echo "<td>50</td>";
echo "<td><input name=\"50\" type=\"text\" id=\"50\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>250</td>";
echo "<td><input name=\"250\" type=\"text\" id=\"250\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>1000</td>";
echo "<td><input name=\"1000\" type=\"text\" id=\"1000\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "<td>10000</td>";
echo "<td><input name=\"10000\" type=\"text\" id=\"10000\" size=\"20\" style=\"background-color:#F5F5F5\" /></td>";
echo "</tr>";
}
Todavía no me entra, sigue más abajo.