Hasta La Motion!

Hi all,
I understand that if you take your 3d model and render out an image into nuke. You can "relight" or move the position of the light, thus eliminating going back into Maya to re-position the lights.

This sounds as eventful as the invention of the Internet.
However, I have yet been able to recreate this in nuke. I have watched the foundrys 2.5 relighting.
5 minutes into that video and I was as lost as a flea in space.

From what I understand, (and that’s not much) is that you render out a position pass in a 3d app and somehow when you move nukes light around, the "Image" relights?

I found a vray tutorial about a point cloud node & sampler infotex which created a point cloud of your image?

So confused, so:
1. Do you need to make your image into a point cloud (2.5 D ) to relight it?
2. If not, does anyone know of a good (EASY) tutorial that walks you thru to relight your model?

Thanks,
Lou