Add filters in gimp (Tiger)

How do you add a filter to gimp in mac 10.4 with gimp 2.6.2? I downloaded a normal map filter from http://registry.gimp.org/node/69

I can only see install instructions for windows and linux. It’s possible it won’t work on a mac.

This probably won’t help:- http://blenderartists.org/forum/showthread.php?p=1248873