ccgi folder for .php files?

[#1]

I am publishing a site for a friend and this is the first time I have used plusnet
I have a little piece of javascript code that calls in a file into a scrolling text box.  nothing clever just a nice simple way of adding interest to a page, so I thought.
I have used this code several time on other website on other servers with no problem so I am having difficulty getting my head round why it isn't working on plusnet....
the javascript code is
<script type="text/javascript">
var iframesrc="news_files/external_2.php"
document.write('<iframe id="datamain" src="'+iframesrc+'" align="center" width="220px" height="120px" marginwidth="0" marginheight="0" hspace="0" vspace="0" frameborder="1" scrolling="no"></iframe>')
</script>
the file external_2.php includes the php code
<?php
include ('latest_text_2.html');
?>
and latest_text_2.html contains the text the users can update for themselves to change the text that appears in the scrolling text box.
So when I publish to plusnet, and run the website, it tries to open the file external_2.php and nothing appears in the text box - very annoying ....
the support section have told me to publish to the ccgi folder, but cannot tell me which parts of the code to put in the ccgi folder and how to then call int he code into the website......
I am really struggling to get my head around how this is supposed to work.....
any advise will be much appreciated.
thanks

[#2]

It is not a cgi folder but a ccgi server that is being referred to.
PlusNet have 2 webservers, one for running simple .html pages and one to run .php pages.
www.username.plus.com points to the www or homepage server which cannot run php code. FTP access is via ftp.plus.net.
ccgi.username.plus.com points to your ccgi webspace which can run .php as well as .html. FTP access is via  ccgi.plus.net.
You have to enable the ccgi on your account via the website settings on the member centre page.
Have a look at the help & support pages related to ccgi and the usertools tutorials (see link in sig) which explain about the shell access (command prompt) to the ccgi webspace.