L3DT - will generate heightmaps, attribute maps for textures, normal maps, and some other things too. I have no idea what a detail map is (the above explanation sounds like an attribute map to me?), and a google search doesn't help.
edit: Oh. Apparently you're already using it. Didn't see your other thread until after this one, in that case if you already have that program, then you are already pretty much set for terrain making. I'd be interested where you got the phrase "detail map" from, because it doesn't appear to be a very conventional one.