Código HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Formulario</title> <script type="text/javascript"> function alertselected(selectobj){ //alert(selectobj.value); var val=selectobj.value; switch(val){ case '0': alert(selectobj.value); capaConsultar.style.display = "block"; break; }; } </script> </head> <body> <table cellpadding="0" cellspacing="0" width="380"> <form action="#"> <tr> <td>Inscripción a:</td> <td> <select name="inscripcion" id="sample" onChange="alertselected(this)"> <option value="0A">Seminario (incluye exposición)</option> <option value="0">Sólo Exposición</option> </select> </td> </tr> <tr> <td>Importe:</td> <td> <table cellpadding="0" cellspacing="0" width="100%"> <tr> <td> <table cellpadding="0" cellspacing="0" width="100%" id="capaConsultar" style="display:none;"> <tr> <td>$30</td> </tr> </table> </td> </tr> </table> </td> </tr> <tr> <td> </td> <td> <input type="submit" value="Subir" /> </td> </tr> </form> </table> </body> </html>