I am using iBook G3 600MHZ and am satisfied with Version 2.5

The new 2.6 Beta says requires G4 800MHZ. I may not be able to use that. Any suggestions?

Move old Skype to a separate folder away from the Applications folder (and the dock link if you have one). Install Skype, give it a try, if you like it, great, if not, move the new one into this new folder, and drag the old one from this folder back into Applications. Skype installs by just dragging into the Applications folder, so you can drag one out, drag another in and try. Don't forget your Dock display. Saved my bacon when an updated version did not work as well as the older one, restoring earlier version avoided lots of hassle!

Every time you upgrade, if you have the internal of external storage space, keep the older Skypes. You never know if they are going to be useful!

You should be able to run in on G3 also, but do not expect that video will work.