First of all, do something about the size of those letters in your signature. They make you look like a twelve-year-old. Secondly, there seems to be no clear correlation from the thread title to the post itself. Not to the untrained eye at least. I happen to know what you are getting at, but if you are looking for help you might want to be a bit more clear about such things.
First of all you have to understand that the files involved, for which there are indeed Nvidia plug-ins for Adobe Photoshop, aren't your usual image files. Perhaps you are trying to edit them without Adobe, or with Adobe but without the right plugins.
NVIDIA Plug-ins for Adobe Photoshop (Normal/Cube Maps, DDS)
If you scroll down a bit on that page you'll see what I mean. Without the plugins for adobe or the right tools to extract the .dds images, it's a little like opening an animated .gif on ms paint; you'll only see the first image while there are in fact several.
This has been a long time for me, I don't know how the supporting tools have changed. Adobe probably has made things easier now, I guess that link I gave you will assist you there. But if like me you don't have Adobe Photoshop to toy around with, there are alternatives. And if you do, it's probably a good idea to get at least the gist of what the plugin does.
You'll need to Google for a tool that can extract the mipmaped images, the differently scaled images contained within the .dds. You'll need to edit those and then you need that same tool or another to compile those images into a new .dds. That .dds is something you can work with. As for the actual editing, you can either edit each individual mipmap, or you can edit the largest mipmap image and resize it to replace the smaller ones.
The Googling is part of the experience, sorry. I'm pretty busy.
