dont doube post!
i found this (in 20 seconds)
http://www.aim.com/help_faq/common_problems.adp
# If you prefer not to have AIM integrated into Outlook Express, go to the Sign On/Off preferences category in AIM and disable the "Make AIM my default instant messaging program" option. Restart your computer if the change is not taking effect after exiting AIM and restarting Outlook Express.