What kind of type are these classes?

[eluser]BrianDHall[/eluser]
A helper is not a class, just a collection of functions that can be used independently of any objects.

A library is what you are looking for, it's the term for where you store your own created class files and such.

A model involves application data - storing, retrieving, processing the 'state' of an application.

So you'd stick your desired classes in libraries folder in the application directory and load them in a constructor with $this->load->library() calls.