Well, to get the same focal lenght of a 10x zoom point and shoot, you must multiply the wide end of the camera, which is most of the times 35mm 10 times, which gives you 350mm, then divide by 1.5 for Nikon, which is 233mm, so yeah, something with 200mm at the long end will be sufficient.
i second the 18-200mm from Nikon. I am a canon guy but a friend of mine has it and he is very satisfied with its performance, taking into account the enormous zoom range.
You can go with a two lens setup, which would be cheaper and yes, the 55-200 would fit nicely with your 18-55.
Sigma has a 18-200 lens, a lot cheaper than the Nikon equivalent, with OS, like Nikon's VR, but I don't know of its performance.