Deform Animation (lattice?)

I am trying to deform a rectangular prism in a certain way.

I really like the effect that a lattice has on it, but I cannot seem to figure out how to set a keyframe to two different states of a lattice.

I tried using an armature to deform the lattice (which would then deform the rectangular prism), but posing the armature has no effect on the lattice, and Weight Paint is not available for lattices.

Is there a way to do this? Or, is there a better approach entirely?

Thanks in advance.
-rking

You can use Shape Keys to change the lattice mesh and then keyframe the influence to animate the change from one shape to another.

Richard:

Perfect!

I apologize for not knowing about Shape Keys. I promise to do my best to avoid abusing this forum by asking too many basic questions.

Thank you.

Quick demo of shape keys for a lattice http://screencast.com/t/kfg9ZL4HMicN

Richard: Thank you. That screencast is very useful.
-rking