This was one of my weirder computing experiences.
I was testing iChat AV, connecting my G5 iMac to my MacBook through our wireless LAN. I was surprised to learn I could use our Gmail accounts for identity establishment.
The connection worked. I showed up on both sides of the video conversation, seen from different angles. There was something odd going on however.
The person I was seeing seemed less and less like me. The image was ... drifting ... in time ... backwards.
Soon I was looking at myself on one screen several minutes in the past.
Eerie. I felt as though I was seeing myself in another space-time continuum.
I have a feeling that the G5 isn't going to cut it. I think iChat might have worked with the G5 under 10.4, so I'm a bit suspicious about Apple (again)
I'll try with the AIM account to see if there's a difference, but I think the accounts are only used to locate IP addresses and ports so I don't expect anything to change.
Update: I tried the Bonjour chat discovery approach; it works on a LAN. There was no change -- the G5 pegged the CPU and gradually fell behind. I then set a bandwidth limit on both clients. At 200 kbps the G5 was able to keep up but the image was obviously inferior. At 500 kbps the image was pretty good, but the G5 gradually fell behind, after about four minutes the lag was pretty severe.
I also tried the Chax Input Manager to modify iChat preferences. I wanted to see if I could use it to make it easy for me to access and control my mother's Mac Mini. Unfortunately when I tested with Bonjour Chax prevented a connection. When I removed it the connection worked. Input Managers are often problematic, so I removed Chax.
So the good news is that there's no need for an AIM account any more -- a Google account works well. The bad news is that the G5 is pretty limited and that Apple's iChat doesn't degrade gracefully. Google's Video Chat does a far better job of adjusting to machine and network capabilities, but it's even less elder friendly than Apple iChat.
Update 2: On the same LAN I connected the MacBook to a 5 yo XP box -- an older machine than the G5 iMac with Google Video Chat. Both machines used the superb Logitech Quickcam Vision Pro webcams. (GVC won't run on the iMac, but in theory the iMac G5 and the old dual core CPU in the XP box should be comparable). GVC absolutely spanked iChat -- it was a far better experience. Unfortunately while iChat is not particularly elder friendly, Google Video Chat is absolutely elder hostile!
PS. Apple's Discussion Forum for iChat is for the 10.4 version of iChat AV. Abandonware?
Update 5/30/09: Just to add the general iChat debacle - if you enable any sort of "parental control" for an OS X account, even if you just lock the Dock, then iChat Jabber and Google Talk account options are mysteriously grayed out. No documentation, no explanation. What a steaming pile.
Update 7/13/09: How to configure auto-answer for iChat.