Hi,
Adding 1+ 1 here.
for the Points
More info that might help.
When you buy a Mac it will come with the current version of the OS (Until recently named after big cats)
How far a Mac can be updated in terms of a New OS can depend on whether it is a Power PC (PPC) computer with G4 or G5 Chips (Processors) on Intels.
There is obviously some cross over with some models being Intel and other being G5s for a while.
Leopard (OS X 10.5.x) will work on both types of computer, but is the last one a G4 or 5 can run.
The version after that called Snow Leopard will only work on Intels
Your version of iChat can be seen by going to the Menu for the app name and About iChat in the Drop down.
My Messages app version of that menu
On AIM valid Names from Apple.
Apple have changed the email ID they issue along with the Service that they have run at the time.
The Earlier @mac.com names came from the .Mac service.
You could have a Trial Account and the name would stop as an email and access to the web site you got but would still work for iChat/AIM.
Obviously Paid for accounts worked and so did Lapsed accounts.
Then Apple changed to MobileMe and issued @me.com names.
These also worked in AIM.
In some cases people linked for email purposes their paid for @mac.com names and the new MobileMe @me.com names.
However this gave them two AIM valid IDs
Also during MobileMe Apple kept the @mac.com registration page for "iChat Names" issuing @mac.com names that only worked as AIM valid IDs
Since then Apple have changed to iCloud.
This meant you had to link an existing ID to iCloud.
In the beginning they issued @me.com IDs (it seemed that they "moved" @me.com ID from the MobileMe Server to the iCloud Server for those with @me.com names already).
Later they issued @icloud.com names.
As I mentioned iCloud linked IDs will not work in iChat 5 or earlier.
As some people could have three Valid AIM Screen Names based on their Apple their appears to be some consolidation going on with all version not being able to use @mac.com or @me.com when talking about iChat.
In some cases you will need to register for an AIM name instead as an updated Apple ID (iCloud linked) will not work.
8:12 pm Friday; July 11, 2014
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
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