User:Ventus
Hey. The GIMP works great for editing different kinds of image files, it has as many features as Photoshop (or more), and it's free. I use this program and only this one for texturing and retexturing.
This has download links:
[Modding Toolbox from my texturing tutorial]
And if you need to know more about normal maps and using the plugin with GIMP, that's in that tutorial as well.
Good luck!