[url=http://harrypotter.wikia.com/wiki/Animagus]

[i]Only very powerful and skilled wizards and witches are able to become Animagi. The process of becoming an Animagus is long and arduous, and has the potential to backfire and cause the transformation to go horribly wrong. Many witches and wizards simply feel that their time might better be employed in other ways, as the skill is of limited practical use unless one has a great need of disguise or concealment. Once the initial training is over, an Animagus can change at will, with or without a wand.[/i]

Just says very difficult training is involved. Nothing about a potion.

However, it would be awesome if they learned how to do it together. They could sneak into the restricted section together or something xD