Hi,
This was using Bonjour.
I have used AIM and Jabber accounts across them as well in separate tests.
I am the Admin on all three computers.
when I set them up I used "Ralph Johns" as the User name.
As a consequence all three were names as "Ralph Johnss Computer" when looking in System Preferences > Sharing. (yes certain OS versions do silly things with names that end in s)
Sine ce then I have made sure they have different names so that they appear in the Shares in the finder.
The G4 tower is in fact "Ralph G4", the iMac is "Ralph's iMac" and the MacBook Pro is "Ralph's MacBook Pro" which also distinguishes it from my son's MacBook Pro ("xxxxxxxx's MacBook Pro").
That is to say that each computer has it's Own Name to use with Bonjour as well as it User logged in to the Mac having his or her own My Card in the Address book or Contacts app.
As I said (well I hinted really) I have also tested in Tiger (the G4 used to have multiple boots up until recently.)
Although Text Chatting is fine Video and Audio chats are more difficult.
In the testing I did do before the drive failed I always had to Video Chat Calling from the Tiger end (G4)
I have seen people report issues when using an Address Book held on a Server where the My Card is then generic.
I do not know enough about Server sets up s to help resolve that.
Try posting in the Server Communities.
8:41 PM Thursday; April 11, 2013
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously