Hi Garygg:
Offical support information from Apple:
System Requirements:
* Macintosh computer with a 600MHz or faster PowerPC G3 or any PowerPC G4 or G5 processor
* iChat AV software (Included with Mac OS X Panther)
* Mac OS X v10.3 or later
* Broadband Internet connection (128Kbps or faster transfer speeds)
With a 3rd party application called Power Boost, it supports your G4 with an iSight for multi-video chats.
http://www.ecamm.com/mac/powerboost/req.html