DXTBmp is a texture converter. You will need that to convert your textures for editing & back again to use in the sim. I believe this is CFS3.

You will need a decent graphics editor (paint program) for the actual repainting. One of the better freeware examples is Pixia. It's posted here at SimV or you might like to check out the home site. http://park18.wakwak.com/~pixia/