Apple recently released a system update for Mac OS X 10.5.2. Included in this release are a bunch of improvements for iChat that impact AIM.

• Addresses an issue with simultaneously-logged in accounts in which iChat sounds generated from one account might be heard in another account.
• Fixes an issue in which iChat idle time is affected by Time Machine backups.
• Improves connectivity when running iChat behind a router that doesn’t preserve ports.
• Enables logged chats from previous versions of iChat to open faster and more reliably.
• Addresses an issue with text chats in which users may be unable to receive messages from the sender.
• Addresses an issue that may prevent rejoining an AIM chat room without reopening iChat.
• Addresses video chat compatibility issues with AIM 6 and third-party routers.
• Fixes an issue with case-sensitivity of AIM handles.

Video interop between AIM and iChat should be much improved, check it out.  Here is the full change log.