You can place login box where you want just must place good patch ( action="index.php?page=loginz&login=1")
box code:
CODE
<form method="post" action="index.php?page=loginz&login=1">
<span class="input-group-addon"><input type="text" class="login_input" name="username" value="{$lang['username']}" onfocus="if (this.value == '{$lang['username']}') this.value = '';" size="12" /></span>
<span class="input-group-addon"><input type="password" class="login_input" name="password" value="pass" onfocus="if (this.value == 'pass') this.value = '';" size="12"/></span>
<input type="submit" class="submit_login" value="{$lang['login']}" />
<span class="full_inb"> <input type="checkbox" name="temporary" value="on" id="fp1" /> {$lang['Temp_login']}</span>
</form>
For example :bootstrap modal window
just use JS