PHP in Templates and Template Conditionals

[Destroy666]

Well, sorry, but I'm not entirely sure what you want to achieve. To block groups let's say 2 and 34 from viewing the nav PM links use this in usercp_nav_messenger:

<tr>
<if !in_array($mybb->user['usergroup'], array(2,34)) then>
(... replace this with rest of code which had been before except trs and tbody, so tds etc...)
<else>
<td class="trow1 smalltext">
{$lang->pms_disabled}
</td>
</if>
</tr>
</tbody>

Still don't know why you want to use $mybb->settings['enablepms'] so I removed it because it made no sense for me there.