The .x importer is broken in 1.6.1.
But probably you will want to use chicken, since it’s a lot more powerful.
Did you restart blender after you extracted the scripts? Also are they in the correct place?
For me, I extracted the chicken files in /home/pro-rsoft/.blender/scripts/. Don’t forget to extract the entire zip (so that the files in scripts/bpydata and bpymodules are in the correct place too!)
It seems just extracting in scripts directory is not enough,I had to place chicken_interface.py file in ~/.blender/scripts/bpymodules/ with executable permission.Your hint of placing files in right places helped.