@mickahtec: Are you trying to edit JPEGs, NEFs, or DNGs? Have you updated your Mac OS to the latest version, which can handle the D7K raw files? Also, what do you have checked under the ADVANCED tab in iPhoto preferences? Is the "use RAW file in external editor" checked off? Your other complaint about not being able to view photos in NX2 is pretty vague (although ultimately I suppose it might be the source of your other problem if NX2 is not installed correctly) so perhaps you could be more specific in describing the problem. I assume you can bring up View NX2 as a standalone app and that after you launch it you can see your folder/directory tree. After you select a folder, you should be able to see the files in it, e.g. thumbnails in the filmstrip along the bottom of the NX2 window plus a normal sized display of the first file in the main viewing panel. There is a little icon near the top left-hand side of window that lets you switch between different NX2 view modes. I assume you've played with that, too. Out of curiosity, have you used the NX2 uninstaller to remove the Nikon app and then reinstalled it? It's hard to see what could go wrong with such a simple install. It certainly worked without a hitch for me on my Mac.
UPDATE: I tried to edit a photo in my iPhoto library using View NX2 as the external editor and experienced the same problem as you had. NX2 came up within iPhoto but could not see any individual photos inside my iPhoto library. In fact, the iPhoto folder was not even listed in the directory tree that's displayed within NX2. Apparently NX2 does not recognize Mac OS X packages like the iPhoto library. Because of this limitation in NX2, you will not be able to use it as the external editor within iPhoto. I also tried invoking Adobe Photoshop CS5 as my external editor within iPhoto. It worked just fine. It's a much better image editor than View NX2, although NX2 offers the advantage that it allows you to access and inspect more of the metadata in the photos from Nikon cameras.