Gimp isn't very good. Use Paint.NET, it's free, too, and it can open .dds files. Though it has its own problems. Texture files with sub-level alpha maps (like Lucario's) don't load properly, but I suppose it's better than nothing.
One way or another, if people are serious about modding they should get the proper tools, and that mean at the very least Photoshop.
If people are curious, my personal workflow uses Photoshop CS6, Paint.NET, Manga Studio EX, Honeyview, 3DS Max and Autodesk Maya. All that to make a single mod.