Gaim: The game for AOL Instant Messaging on Linux
Gaim incidentally is a perfect demonstration of open source at its best, originally started by one developer, it has evolved into a project involving several people, and which continues to develop further and further, despite the fact that the original developer has not worked on it for a long time. Gaim is also currently involved in dispute with AOL, the latter has served a notice on the authors for creating a name 'confusingly' similar to AOL's AIM. Catch up on the latest at their site.
Gaim is available from www.gaim.sourceforge.net. As always there are a number of packages you can choose from and if you can't get one specifically built for your distribution you could always go with a source tarball. Also Gaim is bundled with a number of Linux distributions, so look around, you may just find it already there (try typing Gaim in an X terminal). If you are of course running an old version of your distribution you would probably want to go over to the site and pick up the latest copy of Gaim, so that you don't miss out on all the cool new features.
Once you have it installed, open it up and we're ready to proceed. For Gnome users, you'll find it conveniently installed in your programs menu. You may also want to set it up as a dock app, so that it'll always there when you power up your machine, and of course automatically starts when you connect to the Internet. To add the Gaim dock app, right click on the panel, choose Panel, Add to panel, Applet, Network, Gaim. You'll find a little icon depicting the online/offline status of Gaim. Double click on it to start it up. When Gaim starts you'll be presented with a log in screen which earlier users of AOL's AIM should be surprisingly familiar with.
If you've used AIM before, you'll already have a screen name and password. Key it in, click on sign on and you will be on your way to signing in. If you need to create an account, simply use the register option and you'll be taken to a page where you can do that. If you wish to use multiple accounts, click on the accounts tab and it will help you take care of that. Once you are done, click on sign on and you'll be logged in.