>I am anticipating adding a D700 to my stable. If I use the >12-24 Nikon DX lens on a D700 can I use it as a full frame >18-24 and over-ride the D700 going to the 5MP DX mode?
Yes, you can choose the image area through the camera menu rather than have it done automatically, if you wish. The 12-24mm will cover the whole FX frame from around 18mm upwards, though bear in mind that the lens wasn't really designed to be used in this way and edge quality may suffer a little compared to using it in DX mode.
>2nd Question: Is the 24-120VR packaged with the D700 a decent >lens; that is, at least as good as a 16-85 or 18-200 on a D300?
You'll get varying opinions about the 24-120mm VR, which may be because different people have different expectations. I have no complaints about my copy, which on a DX camera performs a little better in terms of sharpness and contrast than my wife's 18-200mm. I'm looking forward to trying it on my new D700
And I have made exactly the opposite experience: My 18-200 is superb (at least compared to its price, it cannot meet the 24-70, but come close to it), my 24-120 VR is not that great. I have already seen worse lenses, but I don't use it often. Some people report large tolerances from sample to sample, actually that's something I always doubt. I have used the 24-120 VR on film and wasn't really pleased, then on DX bodies with about the same result. And, honestly, since I do have full frame, I never attached that lens, but may give it a try. If you want to have it as cheap as possible, you might also consider some 3rd party lenses. Some are good (but most of the cheaper ones not really great), some are not.
Turtle and hare. After reading so many disparaging comments about the 24-120 VR, when I got my 24-70 2.8 AF-s I did a comparison and frankly found it difficult to see a major difference in decent light. And handheld low light under 1/30 second the good lens looses it's advantage to the little VR lens.
If you are going to compromise files to less than full resolution, or need slow exposures definately go for it. I got mine off eBay on a fluke $200 purchase (slow weekend and seller with one picture) and will probably relegate it to the D70s but it's light weight, low price and ability to take great 1/8 second images make it a keeper. I wouldn't buy a new one though but try used with return rights.
I've always been satisfied with my 24-120mm. It certainly isn't as sharp as my 28-70 f2.8, but it's still good and it serves a different purpose. It has a great range for a "walking around" lens - good wide angle to short telephoto. The VR more than makes up for its 3.5-5.6 aperture range. Actually, I usually use the VR for interiors where I'm likely to be using the lens as a wide angle, so it's only a half stop slower than my 2.8 lens. The VR also makes it possible to stop down a little more than I otherwise could, which helps the performance. For the times when I just want to have one lens on the camera and explore, this is my first choice. I put more emphasis on composition than on what an image looks like at 100% magnification on a monitor, and the 24-120 gives me the range I want for framing an image. I got it to use with my F5, but that's not my favorite "walking around" camera. The zoom range wasn't what I wanted for my D200. With my D700, I think it's a great match, and will used a lot more when I want to travel light.
It would be naive to suggest the 18-200 is not an excellent all round lens It would also be naive to suggest in some respects the f2.8 zooms cannot do better. Overall the 24-120 is almost as good as the 18-200. It is an older design, has to cover 24x36 and the corners are interesting soft at 24mm at close focus distances - but much less distorted than the 18-200 at 18mm. Apart from 24mm close up it performs well, especially for the price, but it would be naive to suggest the f2.8 zooms cannot sometimes do better. If you cannot exceed the resolving power of A4 paper using it 1 stop down (or any other Nikon lens) either the lens is defective or you need to look at your shooting technique. If you want A2 excellent corner quality wide open it can be beaten by more expensive lenses - that is one reason why more expensive lenses exist
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.