Well, silly , iPhoto isn't an image editor and I don't know if Nikon make such a thing.
In order of price here are some suggestions:
The Gimp (free)
Graphic Coverter ($45 approx)
Acorn ($50 approx)
Pixelmator ($50 approx)
Photoshop Elements ($75 approx)
Or, literally, any word processor - Pages. Word etc