Make sure that AIM is completely exited. Don't just sign off, you need to exit AIM completely. Either click on the buddylist on AIM menu>exit AIM, or right-click on the icon on the bottom-right in the system tray on "exit AIM".
C:\Program Files\AIM6\services\imApp\your_version\content\bl\ aolBuddyListAd.js
Open up this file in notepad, hit ctrl+f, and search for adcontainer. The first result is the one you want to change--change collapsed=false to collapsed=true. Save and close the file.
C:\Program Files\AIM6\services\imApp\your_version\resources\e n-US\strings.xml
Open up this file in notepad, hit ctrl+f and search for bl.aimadrotateinterval. Make the four lines look like this:
<string name="bl.AimAdRotateInterval">0</string>
<string name="bl.adMagic">0</string>
<string name="bl.adHeight">0</string>
<string name="bl.adWidth">0</string>
Save and close the file. That's it!