maps share DTX files. some are exclusive to one map however.
for intance. there is a snow DTX that is for both snow valley and cold seed.
how ever cold seed has a second DTX which is kinda ice/snow, which is exclusive to cold seed.
the way i do it is,
go in game and explore the map, look closely at the textures you want to edit, screen shots are good too, that way you dont have to go back in game to look at something you forgot to check, like what shade of blue(example color) it is.
then copy ALL of the DTX files and paste in project>textures.
match the preview in DEdit to the screen shots, and find the one you want, and then export as tga.
NOTE: this is for NON photoshop way, posted by D worm in this section. I haven't read or even looked at why06's thread. so i have no clue if it works for photoshop method. i dont know is photoshop method even uses DEdit.