@cgsipaul said:

I downloaded LibFredo6 3.6b and Curviloft 1.1a. Using SketchUP 8 on a Mac OS 10.
Loaded the plug-ins into the Library-Applications-SketchUp-Plug-Ins folder.
Restarted computer and application, but I do not see any reference to the plug-in.
What am I doing wrong?

Extract it to a different folder then move it to the Sketch Up plugins folder. This worked for me.