In the next few days, Google and AOL are working together to change the way you connect to AIM buddies within Gmail. After this change, Gmail and AIM users can talk directly to each other without having to log into both services (you will no longer be able to log into AIM within Gmail's "Chat" section).
Now, when you log in to your AIM account in Gmail, you get a message from AOL that links to this page:
Back in January 2007, Google and AOL announced that "Google Talk users and AIM users will be able to communicate with one another" and two years later Gmail Chat integrated with AIM, but they didn't become interoperable.
It's nice to know that finally, AIM and Gmail Chat (Google Talk) will become interoperable and the Gmail integration will no longer be necessary.