About hacking in database (javascript)

[Sikozu]

I don't know much (to say the least) programming but this code caught my eye

Invalid Username and/or Password!</font></h1></div><center>
 <script type="text/javascript" src="http://www.dragonfire-bg.net/reg/js/sha1.js"></script>
 <script type="text/javascript">
                function dologin () {
                        document.form.pass.value = hex_sha1(document.form.user.value.toUpperCase()+':'+document.form.login_pass.value.toUpperCase());
                        document.form.login_pass.value = '0';
                        do_submit();
                }
 </script>
 <fieldset class="half_frame">
        <legend>Login</legend>
   <form method="post" action="http://www.dragonfire-bg.net/reg/login.php?action=dologin" name="form" onsubmit="return dologin()">

I tought there's a file with the usernames and passwords (too easy) but instead I believe this file sha1.js is responsible for the passwords (über dislikable lol). I've tried js injection and it didn't work so I'm totaly clueless right now. Guess SQL injection won't work too cause the server returns "Invalid username and password"
Is there a way "rewrite" the dologin fuction to display the passwords?

I added "http://www.dragonfire-bg.net/reg/" to src= and action= cause I downloaded the page to mess with it so it's not there in the original code.