M42 Lens adapter for Nikon D40?

I have a fujinon fish-eye lens with what seems to be the m42 mount. I'm hoping someone can clarify what adapter I should get to use it with a Nikon D40. I don't really understand the terminology of infinity focus and flanges… I want the most versatile use ie landscapes and close-up.Preferably if you could post a link with the best option. Cost is not a problem.
ps. I know the auto focus and other functions won't work.

Added (1). I'm not shopping for landscape and macro lenses, I already have the fisheye lens, which seems like a quality one… I'm just wondering whether to sell it or try to get an adapter for it.

Anyone know if this one would work? Http://www.enjoyyourcamera.com/Lens-Accessories/Lens-Mount-Adapter/M42-Adapter/Quenox-Lens-Mount-Adapter-M42-Nikon-F:2243.html

Well for clarity, you need to know that a fisheye sees the world in a 180 degree, hemispherical world.

That means that no matter what the hucksters say about their $40 "fisheye-macro-wide angle lens", a fisheye lens in neither a good landscape lens nor is it even close to being a macro lens. What it is, is an add-on filter/lens that distorts the image enough to make it look like a fisheye, but is not.

Yes, there are adapters for M42 (old Pentax mount) that allow the M42 lenses to be used with some 35 mm SLR and dSLR cameras. In the case of Nikon there's an adapter, but for Nikon bodies that can use AI mount lenses. That excludes any of the entry level Nikon cameras like the D40(x), D60, D3000, D3100 and D5000.

Look on page 98 of your user manual. You will see the limitations when using AI mount lenses

Best landscape lens for your D40: AF-S 10-24 mm
Best macro lens for your D40: AF-S 60 mm f/2.8 macro

This might help you - here's a whole discussion about about using M42 lenses on a Nikon D40:

I think the main problem with M42 lenses is that they won't all focus to infinity on some cameras - so they might be useless for landscapes. And a fisheye is no good for landscapes anyway.