[eluser]TheFuzzy0ne[/eluser]
Whether you're using CodeIgniter, or any other framework for that matter, frames still work in exactly the same way - They just make requests to the Web server (just like any other window in your browser), and then render the content.
My question is what can you do to ensure that your user is indeed coming from the page that contains the frame, and not trying to access the page directly?
Apparently FaceBook use frames to allow users to have a messenger applet running whilst browsing. Perhaps you might want to check that out?