If you want to view your NEF images in Windows Explorer, download this file from Nikon. It works in Vista and Win 7 (don't know about XP?) And the D3100 and D7000 are included. MS has one that will also read Canon files, for those interested.
I have 64bit Windows 7 Ultimate and have downloaded the Nikon "CODEC". All raw file thumbnails are visible. It's been available for over a year and is compatible with all current Nikon cameras and it's free. Get it here:
I bought Windows 7 ultimate at it's launch in October 2009 and downloaded the CODEC in the same month. I think that because the ultimate version has "virtual XP" that may be the reason mine worked. Otherwise I can't comment further I'm sorry. I certainly didn't download a 3rd Party CODEC.
I have Vista 64-bit and installed the codec (knowing it wasn't 64-bit compatible but hoping for a miracle) and I am able to see a few NEF thumbnails in some folders. Anyone know why just a few would show a thumbnail?
Ok, I just discovered something on this. As stated above I installed the codec on Vista 64-bit. I could see only a few thumbnails. What I found today is interesting, you may want to try it.
1. In your image editing software go to File > Open. View the files (NEF) as a thumbnail in the "Open" window. When the images first appear there is a small black bar at the top and bottom of the image. Let the computer scan through all of the images. The black bars disappear as it scans them.
2. Cancel out of the window and open My Computer or Explorer and go to the folder you just looked at in the imaging software. The thumbnails should show up.
I did this with CNX2 and Paint Shop Pro X2 and it worked.