About AIM in Gmail
Gmail chat now offers the option to sign in to your AOL Instant Messenger (AIM) account to chat with your AIM buddies from Gmail. Your AIM buddies will populate your Contacts list, and are searchable just like your Google Talk contacts.
Chatting with your AIM buddies is easy -- just click on a name in your chat list, and start typing.
Note that an AIM account is required to use this feature. AIM in Gmail is not a Google Talk and AIM federation; it's the ability to sign in to your AIM messaging account from Gmail. Gmail uses Open AIM to provide this feature.
Here's more about AIM in Gmail:Signing in and out
Chatting with someone
Keeping contacts visible in the chat list
Changing which AIM screen name you sign in with
Does Google store my AIM password?