Sykpe/ VOIP installation on old G4

I have just acquired an old G4 Mac. It is already running the latest software it can handle (OSX 10:5:8 (Leopard). I would like to use Skype/ any free VOIP. Although I can download software, no icon appears on dashboard & nothing in applications list. NB. I am a complete novice & non-techy so step-by-step, non-jargon would be really appreciated. Many thanks .... barbsneedsyourhelp