mod_rewrite with Joomla CMS

Hi,

I'm using Apache on a shared host and I've set up a Joomla CMS running
version 1.5, in the root folder /cms. I've also set up a phpBB3 forum in
the root folder /phpbb. I'm using a wrapper to show this forum inside
Joomla in an iFrame. The used wrapper URL is /phpbb. This is just for an
explanation of the environment.

This works quite well, but not when phpBB sends out some e-mail
notifications. Every time the mail body contains a link to the forum it
uses a format like:

"
Board URL: http://www.mydomain.de/phpbb
Your account is currently inactive. You cannot use it until you visit the
following link:
http://www.mydomain.de/phpbb/ucp.php?mode=activate&u=54&k=12 6TLUKKGO
"

Those links however call the forum without any Joomla layout and template -
just the plain phpBB forum.

To circumvent this issue I've put an .htaccess into the root with the
following content:

RewriteEngine On
Options +FollowSymLinks
Redirect /phpbb
http://www.mydomain.de/cms/index.php?option=com_wrapper&view =wrapper&Itemid=53&cc612

This redirects each /phpbb link to the wrapper inside Joomla (The long URL
from the example above is the direct call to the wrapper module). But,
since I'm using a wrapper URL like /phpbb, I get an infinite loop showing
the wrapper inside the wrapper and so on. The content is cascading.

So, how can I resolve that infinite loop? And how can I set up the
..htaccess that given parameters of an URL like

http://www.mydomain.de/phpbb/ucp.php?mode=activate&u=54&k=12 6TLUKKGO
are transferred correctly to the phpBB forum, too?

--
cu,
Michael