Not good enough.
The Extensions Manager doesn't delete files, it just disables them. Bantik's advice also leaves some other items in need of killing...

To leave your Macintosh completely cleansed of AOL Instant Messenger you will need to do the following.

Go to your Apple Menu (the small apple icon in the upper left corner of your screen) and select Sherlock (Find File on pre-8.5 systems). Set the program to "Find items on all disks whose name contains..." and search for all of the following items, to be moved to the Trash and killed mercilessly...

- AOL Instant Messenger
(This search should produce 4 items. A preference folder, a user guide, the application itself, and the folder these last two are contained in. Kill 'em all.)

- AOL NetFind.src

- AIM Menu

- Launch AIM

- AIM Promo

- Idle Time

That does it. No more AIM.