Much Longer info Piece.
iChat can use AIM Based names and Jabber Names.
Apple made an agreement with AIM when the first version of iChat came out that all @Mac.com names would be Vaild AIM Screen Names.
At that time Apple ran the .Mac service (precursor to MobileMe) and Paid for, Trial and Lapsed accounts continue to work as valid AIM screen Names.
MobileMe names continue that to the extent that Trial accounts and Paid for accounts work as Screen Names.
The difference is that Trial account names only work for the period of the Trial and Lapsed accounts also will not continue to work.
At the change from .Mac. to MobileMe people could elect to link their old @Mac.com Email address to their new @Me.com address for Mail purposes.
As far as the AIM Servers are concerned though, these people have two Screen Names.
@Mac.com names are now offered (since MobileMe started) as iChat Names even though they don't work as email addreses.
The naming convention of the Apple Names means that AIM allow the @ symbol as a valid character and that other email address can be valid AIM Names.
You will notice that the AIM link Defcom supplied says you can use a Existing email.
With an @mac.com registration you are asked for an Email address to basically form part of the password recovery if you need it.
This email you use cannot be one you have already used to Create an Apple ID.
The @mac.com name is also a Valid Apple ID (And you can't link one Apple ID to another in this way).
The AIM Site also asks for an Alternative email address for Password recovery but it is not essential like it is on the @mac.com registration. It is worth doing though as their Online Password recovery is not as good as it could be.
One further thing on @Mac.com.
Apple allows passwords to be created that are longer than the 16 character limit that the AIM servers can cope with so you have to keep the Password to 16 characters or less.
These tend to be referred to as Jabber IDs
Google run a Jabber server for their GoogleTalk service.
IF you have a Google Mail account and Enable Talk on your Google Account settings you can use your Email (As it shows on the GoogleMail web page you log in to) in iChat as a Jabber Name.
iChat has a separate Google account addition point as the Server they use does not follow the normal Jabber format.
You can use a Jabber ID from a Public Jabber server or a Private Server.
Not many Public Jabber Servers have an On line Web Browser Registration site like AIM or @Mac.com.
Most need you to use Third Party App like Psi.
Jabber apps Like Psi have a "Registration Module" that can help you create a Jabber ID at the server of your choice.
Your ID is then in the from of an Email Type address of username@JabberServerName.ComorNet (it is rarely an Valid Email as well)
iChat will take everything after the @ symbol and make this the Server name.
Googles Server is called talk.google.com (and not googlemail.com or gmail.com) which is why it has the separate creation point in iChat.
This is one Jabber Server list
It is in English on a Spanish site.
You will notice that many of the server names are based on Country codes as part of the server ID.
You may or may not wish to be "seen" to be somewhere else.
The list is by no means exhaustive and you may find others through a Google Search.
You List OS 10.4.11 which means you have iChat 3.
Although iChat 3 does Jabber it does not have the later GoogleTalk Entry point I have been talking about.
iChat 3 will "pull through" googlemail.com (Or gmail.com depending oon your Mail account name) as the Server name and you have to manually change it. The Instructions have pictures.
OS 10.4.x and iChat 3 were also released before MobileMe came out.
1OS 10.5 got an Update to change the former System Preferences > .Mac pane into one for MobileMe
OS 10.4 did not get this.
One of the things this update did was change and Add MobileMe to all the places @mac.com was listed and this includes the Add Account Option drop down in iChat.
If you have a MobileMe account add it as if it were an AIM name but type the name in full (like as if you used an Existing Email in an AiM Registration)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.7)
Mac OS X (10.6.7),
"Limit the Logs to the Bits above Binary Images." No, Seriously