Hello,

I use Windows XP.
Here is the problem:
Suppose I have a directory named "X" containing files y and Z, and in another
PLACE a directory of the same name "x" containing files y and w.
Then if I drag the first directory to this place, the file y and z takes place in the
second directory (as desired), but the file "w" in the second directory do not disappear (as not desired). In other words, dragging directories do not overwrite directories of the same name, but only add files.  
What setting can I do to make this happen?  

Thanks.
Are you saying the files of the same name are ALWAYS going to be identical in content and you always want to override the file in the directory to which you're dragging another directory?  In other words, y in directory 1 will always be the same as y in directory 2?  If so, what created the duplication in the first place?

And, since no file named "w" was in the directory to which you were dragging a directory, why would you want w to disappear?  Whatever the reason, I believe you'll have to do some manual screening.  If you really don't want w, then you NEED to manually delete it.