Sure. There are two Library folders on your HD; one for the System and one for your profile. In each of those folders is another folder called Preferences.
Inside you will find a whole bunch of files with the ending .plist. These files hold all of your preferences for the programs they are associated with.
What you want to do is find the one that is for AIM and delete it. The next time you open AIM, it will be like opening it for the first time on a new machine. The .plist will return and will hopefully fix your problem.
And you dont have to worry about deleting the wrong .plist. They will return the next time you open the program they are associated with.
Hope this helps.