load modules

[eluser]klompie[/eluser]
I'm building a simple CMS.
Users can edit the content of their site using an admin panel. This content is than displayed on the page.

Now i want to be able to load modules, like an photo album, within this content. I want to use tags to place this modules in the content. Like {photo_album}. How do I parse this? How to replace this tag by some other dynamic generated html.

[eluser]klompie[/eluser]
I found this function, which could be very usable for this i think: http://nl3.php.net/preg-replace-callback

How do i implement this? Where should i store my modules?
Just started with code igniter. Also still learning OOP.