I've try many CMS flavors like MODx, Drupal, Joomla for the admin Panel but they can't seem to manage my existing data, like the users.
I'm planing on building some kind of control panel for my site, similar to the one that is used for managing users and other non-content related items in a CMS. I was wondering if there is something out there which I can start working with instead of starting from scratch.
UPDATE: To do simple tasks like:
I was looking more into a graphical interface more then a system as i have lots of costume content and data like the users.
Now that the question has cleared up a bit, here's a starter's manual for a PHP CMS which takes you by the hand, but from scratch. It starts out with managing users, which seems to be what you're after.
Since you're talking of hosting a lot of pictures, you may want to look up the more than excellent Gallery 2 from Menalto, which is an open source picture management system, but goes much further than just that. It's written in PHP and very actively maintained.
Finally, a list of open source CMS's, of which most of them are written in PHP.