insertar valores de variablen en tabla mysql

[alg76]

Gracias por contestar a mi post.

Este es el código completo:
<?php
session_start();
$db_user = 'user';
$db_pass = '123456';
$user_name = $_POST['user_name'];
$password = $_POST['password'];

//connect to the DB and select the "users" database
$connection = mysql_connect('localhost', $db_user, $db_pass) or die(mysql_error());
mysql_select_db('mi_bd', $connection) or die(mysql_error());


//set up the query
$query = "SELECT * FROM users
WHERE user_name='$user_name' AND password='$password'";

//run the query and get the number of affected rows
$result = mysql_query($query, $connection) or die('error making query');
$affected_rows = mysql_num_rows($result);

//if there's exactly one result, the user is validated. Otherwise, he's invalid

if($affected_rows == 1) {
$ip = $_server['REMOTE_ADDR'];
mysql_query("insert into 'entradas_users' (usuario,direccion_IP,hora) values ('$user_name','$ip',NOW()");
Header ("Location: index.php");
$_SESSION['username'] = $user_name;
}
else {
Header ("Location: login_error.php");
}
?>

he revisado el código pero no consigo que funcione aún con las indicaciones que tan amablemente me has dado...