You're welcome.
neilfrommd wrote:... wondered if iSight could expand utility of the old computer running 10.4; ...
If it still works, your old iSight should still offer every function that it every gave you without any changes whatsoever.
You can only "expand" your 10.4 Mac's utility if you upgrade the OS X system software and/oradd application software that offers functions that your current configuration does not include.
neilfrommd wrote: ... From your responses I think I could use Skype...
You can if you have OS X 10.4 compatible Skype software on your old Mac. If you do not, you can lookfor a Skype that is compatible with all of your system elements.
neilfrommd wrote: ... perhaps the new video chat service that Mozilla is introducing with the latest Firefox ...
No. System Requirements for the latest Firefox show that PPC Macs are not supported. Minimum Mac OS X is 10.6.
neilfrommd wrote: ... (assuming that translates to the Firefox alternative for G4s). Sounds like more effort than I ned to make...
As you can see from my response to your speculation about Mozilla/Firefox above, assuming is not productive.
Thanks for letting us know that determining the requirements is more effort than you want to exert. Consider whether it might actually be faster or easier for you to determine the requirements than to write your questions here and wait for us to do the research and then write responses.
neilfrommd wrote: ... Maybe I can use the old iSight camera instead as a second camera with my newer Mac running Yosemite(?)...
You can -- IF your old iSight still works.
neilfrommd wrote: ... I don't know if FaceTime can handle two camera inputs.
For some discussion on how to select between connected, compatible, functioning cameras, see these Discussion topics:
• http://discussions.apple.com/thread/6531512
• http://discussions.apple.com/thread/5162798
Message was edited by: EZ Jim
Mac OSX 10.10.1