iChat can join either Jabber services like Google Talk or Facebook's "chat" option (there are loads of other Jabber servers as well) Or it can join the AIM service with AIM names of certain Apple Issued Apple IDs (@mac.com, @me.com or @icloud.com ending names)
Your Address Book (in Lion) holds your Contacts.
The info you have about your Contacts may vary.
Some may have Jabber valid IDs (they will look like emails), some may have AIM valid names.
iChat 6 in Lion also offers the opportunity to use Yahoo names/IDs (to chat to other Yahoo users)
To Text Chat to them (the Contacts) they have to have Screen Name (AIM) or a Jabber ID that you add to the appropriate Buddy list. (It is AIM to AIM or Jabber to Jabber).
For instance this Contact I only have his @mac.com email which is a Valid AIM Name in the Contacts App in Mountain Lion (It's a name change for the Address Book)
It is unlikely that an @mac.com name is still a valid email (They were also given out as Trial Accounts and did not work as emails after that and later were free "iChat Names" and also not emails).
Therefore I can only connect to him in iChat (or Messages in Mountain Lion)
I have to have an AIM valid Buddy list to add the Info to.
Google in GoogleTalk run a Jabber server.
You can add Jabber IDs to this Buddy list.
They are in the form of Username@jabberServerName.com (i.e it looks like and email but in most cases will not be).
Only Google Mail Accounts can be activated for "Talk" at the Google Account settings so not all Google IDs are valid Google talk names/IDs
If you only have the one Jabber/Google Buddy list then your Buddies/Contacts need to be using Jabber IDs
Or you need to get a registration with the Service they are using (if iChat Supports it).
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
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