mira, yo te recomiendo que utilices:
Código PHP:
<?if (isset($_SESSION['username']{
echo "bienvenido".$_SESSION['username'];
}else{?>
<!-- Formulario -->
<form action="" method="post" name="form1" id="form1" onSubmit="MM_validateForm('login','','R','password','','R');return document.MM_returnValue">
<table width="200" border="0">
<tr><td class=cap2>Login: </td>
<td><label><input name="log" type="text" id="login"/></label></td></tr>
<tr><td class=cap2>Password: </td>
<td><label><input name="pass" type="password" id="password" /></label></td></tr>
</table>
<br>
<label><input type="submit" name="Submit" value="Entrar" /></label>
</form>
<!-- Formulario -->
<?}?>
saludos