Sorry, I have to talk english now, because I don't know how to explain in spanish. Maybe someone can translate?
I use "TexMod" to modify the textures. For the transparency I use the program "DXTBmp". I extract the textures as .bmp, paint them all green (or black), open them with DXTBmp, create a transparency and save them as .dds. Then I edit the TexMod log file by replacing .bmp with .dds and save it. Then I create the .tpf file.