Chose "Save Picture As" and save the picture to your hard drive.
Go to the menu bar in your Instant Messenger client.
In the "People" menu, chose "Select Buddy Icon".
Select "Browse PC".
Then select the Buddy Icon located on your hard drive.
Macintosh
Mac users must click and drag their icon to a location on their hard drive,
and then select it manually from within AIM's Buddy Icon Preferences.