Thanks for the prompt reply. So there is a version of SU8 that will run on 10.5.8 and allow the use of the .rbz extensions? I haven't been able to find one so far.

@dave r said:

Download the RBZ file, and use Install Extension from Preferences>Extensions. If you don't have Install Extension there, you have an old version of SU8. Install the newest version of SU8 and you'll be able to install the RBZ file.

Download and install the Plugin Store and you can auto install.

Looks like exactly what I need. Thanks! However, I am stuck (for the moment) in OS 10.5.8, and SketchUp v8, so I need an .rb plugin. Might you still have that laying around?