AIM is not free. Maybe free to use, but you need to register at AOL.
There is no official support than for Windows and Mac OS X. You are able to use it with other tools on Linux etc., but that is officially forbidden.
If a user is inactive you can tell this also in IRC(manually or with special scripts). This is not default, but the default way it works in AIM(ICQ, Skype etc.) is very unreliable, too.
And btw. why AIM, not yahoomessenger, windowsmessenger, skype?