Start på login system HELP! :P

<script language="php">
if ($_POST["submit"] == "login") {
if ((isset($_POST["username"])) && ($_POST["username"] != "Brugernavn")) {
if ((isset($_POST["password"])) && ($_POST["password"] != "Password")) {
echo "Logged in";
}
}
} else {
echo "<form method=\"post\" action=\"index.php\">";
echo "<input class=\"LoginTextBar\" type=\"text\" value=\"Brugernavn\" name=\"username\" onclick=\"this.value=''\" />";
echo "<input class=\"LoginTextBar\" type=\"password\" value=\"Password\" name=\"password\" onclick=\"this.value=''\"/>";
echo "<input class=\"LoginButton\" type=\"submit\" value=\"Login\" name=\"login\" />";
echo "</form>";
}
</script>