hey Blackstar, welcome
Right now I am a little dizzy ("special" cigaret), but I think you are trying to edit a .Dmap, which is the wrong file...
to edit a minimap:
*go into your conquer folder
*go to the data folder
*go to the minimap folder
it might be usefull to change your viewing settings to tumbnails, so you can see all the maps,
you can either open the existing map in a drawing program (paint or so), or you can make a screenshot of a ingame minimap with a party star on it, cut out the mini map, and rename it...
hope I am clear enough, else you can pm me...