Código HTML:
<form name="form1" method="post" action="autenticacion.php">
<input name="username" type="text" class="style1" value="Usuario" size="15">
<input name="password" type="password" class="style1" value="123456" size="15">
<input name="Submit" type="submit" class="style1" value="Entrar">
</form>