Good tutorial for morphism?

Does anybody know where I could find a good (and easy) tutorial to implement a simple morphism (like from a cube to a tetrahedron)?

What’s tetrahedron? Ok I found something.
BTW while searching for what’s terahedron (lol!) I found this site with nice stuff in paper

Are tetrahedrons the best point to start with, they don’t seem to be the simplest figures we have, do they?

[This message has been edited by MickeyMouse (edited 12-05-2002).]

There is a paper by Greg Turk called
Shape Transformation Using Variational Implicit Surfaces.