Use XWE, or wintex. Those work pretty good with adding textures in.. At least, that's what I've heard.
EDIT: Oops, I didn't see that part about only using doombuilder. My bad! Sounds like a cool editor though. May try it out for mapping myself.
It's a game. Get over yourselves already. How long are people going to keep crying about this anyway?
Personally I just do what Printz said and turn up the brightness a notch or two, not that I ever had to anyway.