OK, what does your YOURFORUM\include\template\main.tpl look like?
I've used this mod with no problems in the past and this is what the relevant section of main.tpl looks like when I use it:
ETC ETC
<div id="punwrap">
<div id="pun<pun_page>" class="pun">
<div id="brdheader" class="block">
<div class="box">
<div id="brdtitle" class="inbox">
<pun_desc>
</div>
<pun_navlinks>
<pun_status>
</div>
</div>
<pun_include "attention.php">
<pun_announcement>
<pun_main>
<pun_footer>
ETC ETC
And this is the contents of my PUNFORUM\include\user\attention.php, which displays without any issues:
<?php
if($pun_user['is_guest'])
{
?>
<div class="block">
<div class="box">
<div class="inbox"><p align="center"><b>Welcome Guest!</b> To post a message, please <a title="site registration link" href="register.php">register</a>! Registration is easy and free. If you have registered, please <a title="site login link" href="login.php">login</a>.</p>
</div>
</div>
</div>
<?php
}
?>
Another thought: make sure that you have uploaded (via FTP) any files you have modified as ASCII text. What you are seeing might be some sort of binary artefact.