[Xenon]

the easiest way:
look at the sourcecode of the normal loginbox of a vb

from template forumhome_logincode:

<form action="member.php" method="post">
<tr>
	<td nowrap><smallfont><b>Not cookied?</b><br>Login with username and password:</smallfont></td>
</tr><tr>
	<td nowrap><input type="hidden" name="s" value="$session[sessionhash]">
	<input type="hidden" name="action" value="login">
	<input type="text" class="bginput" name="username" size="7">
	<input type="password" class="bginput" name="password" size="7">
	<input type="submit" class="bginput" value="Login!"></td>
</tr>
</form>

just change the design, and be sure the form action shows to the member.php of your forum (add full url path maybe )