Hmm, do you what are the correct IP addresses if not I could do a tracert in cmd and poke around for the right address in the mean time Talk to me if you can get AIM to work on Mac OS 8.1 or any other classic systems.
If you haven't already you might try asking over at the 68kMLA Forums: https://68kmla.org/forums/ or using a different version of the client. Not sure if there are any unofficial clients for MacOS 8 but that might be worth a go too if any exist. Is this the version you're using http://macintoshgarden.org/apps/aol-instant-messenger-47?