[EASY] Best practice for this (MVC)

[eluser]boltsabre[/eluser]

So I should create a helper?

No idea, as I said, it really depends on what you're trying to do. If it's just a function then fine, but if you need to create a class/object then you should do it in a library.
Yes, you can load libraries/models/etc in helpers (and in your own libraries).
But you cannot use $this, it has to be $CI... just google "codeigniter how to load a library in a helper" for more details.