When should I use 18mm-55mm lens and when should I use 55mm-200mm lens in a Nikon D80 camera?

Question

Also what are the advantages of having the 18mm-200mm DX lens? How do you like your Nikon D80?

Answer 1

You use the 18-55 when you may want a wider field of view.

Obviously you use the 55-200 when you may want to zoom in on something further away.

The advatage of the 18-200 DX lens is that you can change lenses less often, and is lighter than standard lenses because they take advantage of the 1.6x EFL change of the smaller sensor.  However, be aware that DX lenses are specifically for the APS-C sized sensor.  If someday you go to a full frame sensor camera (i.e. D3, D300 or upcoming D700) you will not be able to use your DX lens and would have to buy a new one.  

The D80 like all Nikon products is a solid mid-level camera.  The only real drawback to the camera is that it is noisy at higher ISO settings (something Nikon suffered with until the recent release of cameras with the new Expeed processor)

Answer 2

you ue the 55-200 when you want to zoom in further than the 18-55 would let you.  You use the 18-55 when you want more wide angle than you can get with the 55-200.  

The 18-200 is an all in one lens so you carry one lense instead of two.  However, they are usually slower (higher f stop) than smaller zooms and usually not as sharp.