I've been watching GECK tutorials on youtube. I saw the clutter tutorial and the Object Pallet, the guy in the tutorial loaded an opal file and I saw he had dozens of them.

Is there a set of opal data files floating around the internet? Because it would be just as much work to make that many myself as it would be just not to use opal altogether.

Also I need a program that will allow me to view .nif files or extract them from wherever they are so I can use them in the geck?

You don't seem to know much, but NifSkope is what you're looking for.