Hiya.
For a 'detail' on a terrain, I think you add something like:
bmap bumpmap = <detailtexture.bmp>;
ACTION terrain_detail {
detail_map = bumpmap;
detail_size = 5;
MY.AMBIENT=-20;
}
Then, in WED/GED, select the terrain and add the ACTION "terrain_detail" to it as it's BEHAVIOUR. However, if you are going to be using multitexture shaders on your terrain, you probably have to do something else...can't help you there, sorry.
As for a Terrain Editor, I use GROME II (
http://www.quadsoftware.com/index.php?m=section&sec=product&subsec=editor ). A lot of others swear by T.Ed (
http://www.thegamecreators.com/?f=ted ) or Terragen (
http://www.planetside.co.uk/ ), but I seriously considered GeoControl (
http://www.geocontrol2.com/index.htm ) before I decided on GROME II. With GROME II, there is a plug-in (currently in beta) to export to A7 (terrain, textures and objects) that requires little extra work. Pretty good, really.