I meant "joining meshes as shape keys" Basically, you have two meshes; one of them has some altered polygons (like in this pic, her top eye lids were brought down a bit). Under the search menu, you can join them together by selecting the one that you want to be the shape key first, and then the one that's the base mesh.

These are also called Blend Shapes, Morph Targets, and Flex Animations, depending on which program you use. I'm using Blender 2.63

I'm using blender too. Had no idea you could do shapekeys with two models.
No help from me there, sorry XD