AIM for solaris can be found here, but it looks like it is about 10 years old. Most likely AOL dropped support in beta.
http://www.aim.com/beta/javadownload.html
If you don't know how to do much in Solaris, like say install any other program, then you will probably have difficulty with this as well, but the same can be said for someone that has never touched Linux trying to install programs on it.
As an alternative, if the browser in Solaris that you have supports it (you are running Mozilla 1.7, minimum is 1.4), you can try AimExpress, as it does not require an install, and runs off of your web browser:
http://www.aim.com/aimexpress.adp
Sorry, I don't know much about Solaris, but I hope that helps somewhat. Best of luck.