Someone has succeeded in making The Horde work with DosBox? What is the secret?

use the next version of DOSBox.
I've played it in there succesfully.
You should check the dosbox forum (development forum) on cvs builds if you are interrested.

Here is a good guide how to make build games to work in XP enviroment (Blood, Duke Nukem, Redneck Rampage, Shadow Warrior). I have only tried it with Blood and it works excellently.