How can I log into a simple web access login using Python?

I'm trying to create a little Python script that'll log into a web access authentication page for me automatically for the purposes of convenience (the login appears each time the computer is disconnected from the network).

My attempt so far has been to use the module mechanize, but running this doesn't result in the login vanishing from my standard browser:

import mechanize
browser = mechanize.Browser()
browser.addheaders = [("User-agent","Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.10 (maverick) Firefox/3.6.13")]
browser.open("http://ift.tt/S0UJZD")
browser.select_form(name="logonForm")
browser["login"] = "myUsername"
browser["password"] = "myPasscode"
browser.submit()
print browser.title()

How can I get this login to work in Python?

Here's what I think is the relevant section of the HTML of the login page:

<form name="logonForm" style="display:none">
    <!-- Logon Form -->
    <div id="logonForm_subscriptionChoice_top_title_block" class="subtitle">
        <span id="logonForm_subscriptionChoice_top_title_text">YOU ALREADY HAVE YOUR LOGIN</span>
    </div>
    <div id="logonForm_auth_modes_block" style="display:none">
    <table class="hoverLink"><tr>
<td>
                <div id="logonForm_shibboleth_authentication_button">
                    <img src="./resources/_images/shibboleth.png" height="30px"><br><span id="logonForm_shibboleth_text">Utilisez vos identifiants institutionnels</span>
                </div>
            </td>
            <td>
                <div id="logonForm_standard_authentication_button">
                    <img src="./resources/_images/ticket.png" height="30px"><br><span id="logonForm_ticket_text">Utilisez un ticket de connexion</span>
                </div>
            </td>
        </tr></table>
</div>
    <div id="logonForm_logon_block">
        <table>
<tr id="logonForm_logon_block_credentials">
<td class="label">
                    <span id="logonForm_login_text">LOGIN</span><br><input type="text" name="login" autocomplete="on">
</td>
                <td class="label">
                    <span id="logonForm_password_text">PASSWORD</span><br><input type="password" name="password" autocomplete="on">
</td>
                <td>
                    <button type="submit" id="logonForm_connect_button"><span><img src="./resources/_images/auth_button.png" height="35px"></span></button>
                </td>
            </tr>
<tr id="logonForm_policy_block">
<!-- Check Box Confirm (Visible status depends on configuration option) --><td colspan="3">
                    <br><input type="checkbox" name="policy_accept">&nbsp;
                    <span id="logonForm_policy_text"></span>
                </td>
            </tr>
</table>
</div>
    <br><button type="button" id="logonForm_authentication_form_back_button" style="display:none">Retour</button>
    <div id="logonForm_subscriptionChoice_block">
        <br><div class="subtitle">
            <span id="logonForm_subcribe_bottom_title_text">NOT A LOGIN YET ?</span>
        </div>
        <br><div id="logonForm_subscriptionChoice_first_double_insert_block">
            <table class="hoverLink"><tr>
<td></td>
<td></td>
</tr></table>
</div>
        <div id="logonForm_subscriptionChoice_second_double_insert_block">
            <table class="hoverLink"><tr>
<td></td>
<td></td>
</tr></table>
</div>
        <div id="logonForm_subscriptionChoice_single_insert_block">
            <table class="hoverLink"><tr><td></td></tr></table>
</div>
    </div>
</form>