How do I send a POST request without output or redirection?

[BobTheGreat]

I'm making a lightbox thing for a login so I made a lightbox php script and I dont want to redrect so I have to send a HTTP request using JS.
Heres my lightbox code:

<?php
//add lightbox for LOGIN
$loginlb = beginlightbox();
?>
<b>Login</b>
<form name="loginform">
Username:&nbsp;<input type="text" name="username" id="username" /><br />
Password:&nbsp;<input type="password" name="password" id="password" /><br />
<input type="button" name="login" id="login" value="login" onclick="login();">
</form>
<?php
endlightbox($loginlb);
?>

PS I made my own lightbox commands

[acoder]

You'd need to use Ajax. Have you any experience of it?