Hey Allan,
I see you are getting some good feedback - here's a bit more.
While you could get by using this camera and lens on NN3 at the wider focal lengths (18mm) it is very near the upper weight limitations of the product - some sag may occur especially with longer exposures. The lens Nick suggested is a popular one and certainly worthy of consideration if you are favoring full spherical panoramas up to 360x180 degrees using your D5000 on NN3.
Our least expensive option to accommodate your current needs is the NN5L. The stand alone version is only US$329 and even less if you can find one used (contact one of the resellers in your region). The NN5L will not only accommodate your camera and 18-200mm lens but give you much more room to grow later down the room. The image quality of the 18-55 would be better than the Samyang but obviously requires more images to produce a panorama. So the initial investment on your part would be less if opting for the NN5L.
Here is a chart at the bottom of this page to give you a "general idea" of the number of shots required to shot at a given focal length.
http://nodalninja.com/product_selector.html
Hope this helps
keep us posted on how you go
Cheers
Bill