I have to change somthing in system_block_login.html
if i use a custom made theme Right?

What have i to change?

<form style="margin-top: 0px;" action="<{$xoops_url}>/user.php" method="post">
<{$block.lang_username}><br />
<input type="text" name="uname" size="12" value="<{$block.unamevalue}>" maxlength="25" /><br />
<{$block.lang_password}><br />
<input type="password" name="pass" size="12" maxlength="32" /><br />
<input type="checkbox" name="rememberme" value="On" class ="formButton" /><{$block.lang_rememberme}><br /><{* autologin hack GIJ *}>
<input type="hidden" name="xoops_redirect" value="<{$xoops_requesturi}>" />
<input type="hidden" name="op" value="login" />
<input type="submit" value="<{$block.lang_login}>" /><br />
<{$block.sslloginlink}>
</form>
<a href="<{$xoops_url}>/user.php#lost"><{$block.lang_lostpass}></a>
<br /><br />
<a href="<{$xoops_url}>/register.php"><{$block.lang_registernow}></a>

NO

its only if you use a customized system_block_login.html

then you need do modify your custom system_block_login.html

that has nothing to do with a theme.