There is any world builder for CS???
this would save an enormous work. To edit maps in 3dsmax or any another program its much complicated. You does not have much has controlled on the limit of engine...
Personally I would recommend Blender. It is a very good modeller and it supports Crystal Space very well. There is no native CS world builder and personally I don't see the need.
well, at least i can use radiant, isn´t???