Nikkor 55-200 vr good for headshots?

I'm using a nikon d5000, sb 600, and also have a sigma 18-200 which does not autofocus on my camera.

That would be perfect for head shots. Portraiture with a 35mm camera is best with a 80mm focal length. If your camera does not shoot full frame then 55mm may translate closely to 35mm film and 80mm focal length. You'll have to do the math.