A little info that might help you unravel the mysteries of Nikon cameras and lenses :-

Nikon Cameras and Nikkor Lenses.
This information is important to understand in terms of future camera/lens planning.
Nikon camera bodies are either termed “Full Frame” (FX) or “APS-C” (DX), the difference being the size of the sensor. Full frame cameras tend to be for professionals or “extreme enthusiasts”.

Current FX cameras include the D4, D3, the D700 and the newly-introduced in 2012 D800 and D600.

Current DX cameras are the D3000 and D5000 series, the D7000, D7100 and the older D80, D90 and the “semi-pro” D200, D300 and D300s.

Nikon lenses are designated either FX or DX.

A DX camera has an APS -C smaller sensor and lenses with a DX in the title were built specifically for this sensor. The DX designated lenses are made smaller and lighter specifically for use on DX bodies in accordance with the reduced needs of the crop sensor. Nikon allows DX lenses to be used on all their FX bodies, but with reduced sensor size results, or else with extreme vignetting.

FX lenses will work on all DX bodies and give the advantage of only needing the centre portion (sweet spot) of the glass in those lenses, typically giving even better net results than they do on FX bodies. FX lenses are also a much better investment as they will not depreciate in value nearly as much as DX lenses, primarily due to the increasing number of users for these lenses. There appears to be an increasing number of DX users moving up to FX bodies. But you can use FX lenses with a DX camera.
All the forum pundits advise that if you are ever thinking of “going FX” then you should buy FX lenses from the start. So as you start buying lenses, give some thought to this !!
Nikon lenses are either "manual focus" (Ai, Ai-S) or "auto-focus" (AF, AF-D, AF-S and AF-S with a G designation, which are the newest).

Unless you are prepared to learn and cope with the (old-fashioned) “manual method” of focussing a lens you should only look for “auto-focus” lenses. Nowadays many older, but high quality manual focus lenses are available, and often are much less expensive, but they are only for use if you don't mind manual focusing... !

Very important !! ....... the most modern auto-focus lenses have their own internal auto-focus motor. Others need to be driven by a motor for that purpose in the camera body. Only lenses with an AF-S designation have their own internal drive motor. Nikon call it "Silent Wave Motor". All the others need to be used on a camera with its own in-camera motor for auto-focus to work. Nikon D3000/D5000 series cameras do NOT have that drive motor and will therefore only autofocus with an AF-S lens. DX Cameras WITH that motor are the D90, D300, D300s, D7000, D7100 and the Full Frame (FX) models the D700, the new D600, the D800 and the pro models the D3, D3x, D4.

Which lenses are good? The term you will see used amongst many enthusiasts for a lens is "glass" – a terrible affectation in my opinion. All Nikon lenses are good, but some are better than others. You usually "get what you pay for". There are also what is known as "fast" lenses. These tend to be either "primes" (single focal length) or zooms (eg 24-70mm/70-200mm) which have a better capability in low light situations. Look for lenses with an aperture of f1.2, f1.4, f1.8, f2, f2.5, f2.8, f4 - and for zooms it should be the same constant large aperture across the whole zoom range. That is NOT to say that lenses with larger aperture range (eg f3.5 - f5.6) are not good. Many will advise "buy the camera body only, then buy the best lens you can afford". Wise advice which can save you a lot of cash in the long run !