Keyframe animation in OpenGL?

I’m trying to get some action on some models in my app. I basically want to do
w * keyframe0 + (1 - w) * keyframe1.

I’d prefer to be able to do it on the GPU, and to have the keyframes stored in vertex arrays with VAO/VAR if supported. It seams like the GL_ATI_vertex_streams extension will allow me to do this, but I have yet to try. Is there any other way to do it without locking me to vendor specific extensions, or at least a way to do it on nVidia cards too?

Hmm, silly me, I can of course do it in a vertex shader. Though first that it would be impossible since I need two vertex inputs, but I can of course pass the other keyframe as attributes ala