Well, yes, sort of. JRP's comment is correct but incomplete. A fisheye becomes a non-rectilinear corrected wide angle lens. With your rectilinear wide angle lenses, you can essentially just consider the lens to be multiplied by 1.5x so a 14mm lens would have the same field of view as a 21mm lens would on a 35mm camera. Note that the perspective doesn't change from that of a 14mm lens, just the field of view. This is farely noticable with the wide angle lenses. With the fisheyes this especially holds true. So in essense, yes a 16mm fisheye becomes a 24mm fisheye with a totally different look from a 24mm lens. I've attached the crop from the bottom edge of a photo taken with the 16mm Nikor on the D100. Notice how the straight edge of the bar counter is heavily curved, looking almost circular.
DaveDosch Take nothing but pictures, leave nothing but bubbles.