ok, si
Notice: Undefined index: usuario in C:\xampp\htdocs\pm\menu.php on line 7
el index es:
<?
session_start();
if(isset($_SESSION["usuario"]))
{
header ("Location= menu.php");
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="es" xml:lang="en">
<head></head>
<body>
<form action="validar.php" method="post">
<p>Usuario:
<input type="text" name="usuario" size="20" maxlength="20" />
<br />
Password:
<input type="password" name="password" size="10" maxlength="10" />
<br />
<input type="submit" value="Ingresar" />
</p>
</form>
</body>
</html>