To install NTK 1.6.4:
~~~~~~~~~~~~~~~~~~~~~

-Download both files (NTK164.sea.hqx and NTKMac164b3.sit.hqx)
-Expand NTKMac164b3.sit.hqx, follow the instructions therein (dragging the 
appropriate folder)
-Expand NTK164.sea.hqx, it will contain just one file: an updated Newton 
Toolkit executable.  Replace the Newton Toolkit binary in the previous 
directory with this new one.