Making it way way way too hard.
No JavaScript needed, at all.
Boiled down to the bare essentials:
Code:
<form method="get" action="http://yoohoo.com/login_whatever.php">
<input type="text" name="u" size="25">
<input type="text" name="username">
<input type="text" name="password">
<input type="submit" value="Go">
</form>
I don't know what the purpose of your
name="u" field is, but it *TOO* will be send along to
login_whatever.php as part of the URL.
If you don't need/want it, then omit it.