You should install ViewNX 2 from your Coolpix CD that came with your camera.
Download quick media converter from
www.cocoonsoftware.com
It will convert almost any media format, into
almost any media format.
...
Or, you could just download quicktime, but if
you’re not an apple fanboy/girl ... VLC from
www.videolan.org is the best alternative as a
player that will play just about anything.