I have tried using NX2 on an old Pana FZ7 pic, ie .jpg original. The only thing you don't get that you would from a Nikon .nef image is exposure compensation (and tweaks needed for newest Nikons). The pictogram in the 'easy fix' section is similar to levels in that it allows adjustment of over/under-exposure but without changing colour balance. The shadow 'protection' (= recovery in English) is still very good.

So anyone with half a mind to try an alternative to CS3 or new to post-processing altogether might well try it out while its on 60 day free offer.

For acclimatisation I recommend that if more than 'quick fix'is needed, control+B gets the colour balance menu whith sliders on blue-yellow, red-green & magenta-cyan axes and also includes further contrast and brightness correction. If only required for part of the image, choose 'selection control point' from the tool bar with shift key pressed down. This is roughly equivalent to selecting using a 'magic wand' tool but just works better if there is a strong colour boundary.

You can 'save as' .nef despite the original not being one and preserve your first rough efforts to fine tune later without getting a massive file as when using .psd. However you need say 10GB free space on the hard drive for NX to use as cache or it all slows right down.

Do ask questions here