is getting PI 1.6 running on osx 10.5 something you are working on
Yes, I'll try to solve this problem as quickly as possible. OS X 10.6 breaks compatibility of multiplatform applications like PixInsight because it updates the versions of several system libraries, but does not provide the old versions (or symbolic links to them, as is usual in UNIX systems) that were included in 10.5.
I just have to investigate which libraries are causing problems and manually include the old versions in the PI 10.6 distribution. This will happen next week --right now I am having a bit of rest in a nice rural location where I don't have a Mac machine at hand

Sorry for the inconvenience.