asunto arreglado... hice esto...
Código PHP:
<? if ((!isset ($_POST['buscar'])) and (!isset ($_POST['carros'])) and (!isset ($_POST['motos'])) and (!isset ($_POST['lanchas'])) and (!isset ($_POST['aviones'])) ) {
echo ' <form action="" method="POST" >
<select name="buscar" onChange="submit();">
<option>Seleccione</option>
<option value="carros">Carros</option>
<option value="motos">Motos</option>
<option value="aviones">Aviones</option>
<option value="lanchas">Llanchas</option>
</select>
</form>
';
}
?>
</td></tr>
<?php
switch ($_POST['buscar']) {
case 'carros':
print ("
<tr><td> Carros </td> </tr>
<td> <form action='' method='post' >
<select name='carros' onChange='submit();'>
<option>Seleccione</option>
<option value='venta' >Venta</option>
<option value='renta'>Renta</option>
<option value='talleres'>Talleres</option>
<option value='varios'>varios</option>
</select>
</form>
</td>
</tr>
<tr><td> <a href='index.php' class='enlace_imagen'><img src='promos/regrear.png' /></a> </td></tr>
");
break;
case 'motos':
print ("
<tr><td> Motos </td> </tr>
<td> <form action='' method='post' >
<select name='motos' onChange='submit();'>
<option>Seleccione</option>
<option value='venta' >Venta</option>
<option value='renta'>Renta</option>
<option value='talleres'>Talleres</option>
<option value='varios'>varios</option>
</select>
</form>
</td>
<tr><td> <a href='index.php' class='enlace_imagen'><img src='promos/regrear.png' /></a> </td></tr>
");
break;
case 'lanchas':
print ("
<tr><td> Lanchas </td> </tr>
<td> <form action='' method='post' >
<select name='lanchas' onChange='submit();'>
<option>Seleccione</option>
<option value='venta' >Venta</option>
<option value='renta'>Renta</option>
<option value='talleres'>Talleres</option>
<option value='varios'>varios</option>
</select>
</form>
</td>
<tr><td> <a href='index.php' class='enlace_imagen'><img src='promos/regrear.png' /></a> </td></tr>
");
break;
case 'aviones':
print ("
<tr><td> Aviones </td> </tr>
<td> <form action='' method='post' >
<select name='aviones' onChange='submit();'>
<option>Seleccione</option>
<option value='venta' >Venta</option>
<option value='renta'>Renta</option>
<option value='talleres'>Talleres</option>
<option value='varios'>varios</option>
</select>
</form>
</td>
<tr><td> <a href='index.php' class='enlace_imagen'><img src='promos/regrear.png' /></a> </td></tr>
");
break;
}
Gracias por ayudarme ... saludos