Valerio,
If you have not already visited this link,
http://www.birdphotographers.net/for...ead.php?t=5598, I suggest you do so. Artie posted a how-to on creating a JPG for posting here including sharpening recommendations. Besides that he talks about his books and the Digital Basics eBook. At a minimum I suggest the Digital Basics eBook as it will jump start your Photoshop skills. I am gathering from your posts that you are using Capture NX from Nikon.
Unfortunately, I do not use that and cannot help you directly with that, but you might want to search out literature on its use. Try a web search for books on Capture NX. I found one at
http://www.luminescentphoto.com/nx2guide.html. I am not recommending it. It is just one I found them with a Google search.
Also try Nikon's Capture NX website at
http://www.capturenx.com/en/index.html.
Nikon's Capture NX manual for purchase at
http://www.nikonmall.com/detail/NIK+IB+NX2.
This website has links to Capture NX resources and tutorials. I saw one about sharpening in Cpature NX:
http://dptnt.com/2008/09/the-ultimat...esource-guide/
As far as camera technique, it does not appear the image is in focus. Did you use a tripod? Is the lens an IS lens? Was IS on to help you get a sharp image? What camera are you using?
Artie's books, The Art of Bird Photography including the first book reprint and the ABP II on CD, though geared towards bird photography would tell you a lot about handling the camera, etc. As you are interested in landscape, books by John Shaw or TIm Fitzharris (my favorite of his is National Audubon Society Guide to Landscape Photography) will help you with those.