Форумы / Cotonti / Skins / Page-specific tpl?

That should be:

<!-- IF {PHP.pag.page_id} == 22 AND {PHP.usr.isadmin} -->
<span style="display:block; float:right"><a href="{PHP|cot_url('page','c=members&m=add')}">Submit new member</a></span>
<!-- ENDIF -->

not

{PHP.page.id}