[eluser]stuffradio[/eluser]
You waited an hour and bumped your post? Tsk tsk
You should try and separate things as much as possible. If you want to handle sessions like login/logout, maybe have a controller that's called sessions. If you want to have a registration page maybe do a controller called register or registration.
Don't stick all things in one controller as it's less efficient I think. Don't have one model for everything. Maybe make a model for each table, or do a model for different components of your site.
Models: Register -> checkUser()//This would check if users exists
-> checkInput()//This could make sure all input from the form is valid
Login -> checkSession()//Checks if the user is logged in already
Those are examples of how you could organize your application.