Separate the admin php files

[eluser]Alexander Radsby[/eluser]
I understand that it's pretty easy to make CodeIgniter show regular pages such as:

http://www.yoursite.com/about-us/

But if I write a cms system to the site, how do I get the url to be:

http://www.yoursite.com/admin/something?

And is there any way I can separate the admin "controller/views/models" from the regular site "controller/views/models"?