I'm not ure if many here use MSN Messenger, but most know Microsoft abandoned support for Mac OS 8.1, and now you need Mac OS 9.2.2 or OS X to ruMSN, unless you use Mac Messenger 3 which still requires at least Mac OS 8.6 and is still quite crash prone.
I downloaded AMSN from Sourceforge.net which is written in Tcl/Tk, and a complete 8.4.2 Interpreter is available for PPC Mac OS. On my Performa 6300, MSN takes aprox. 1 minute or so to load up, but after it's loaded it's reasonably useable nd I can still run other apps in the background such as MP3, Outlook, CyberDog and more. It's very stable and even when an error occurs the application doesn't quit but gives you the option to silently ignore all errors and just continue anyway.
All in all it is a great program. It's possible it might also run on 68K's as I have not able to use SSL, but managed to connect by disabling it. There are 68K versions of the Tcl/Tk interpreters, but I did not check to see if it is at least Version 8.3 or later, as that is the version of Tcl/Tk that AMSN needs. It might also work on system 7.5.3/7.6.1 and from what I can see, I made a standalone application so no extra installations are required.
If anyone wants the Disk Image I created with the standalone application to test out, let me know and I will arrange to have it hosted. Mainly this is for fun as it's fun to see MSN running on 8.1 and perhaps even some PowerBook users will benefit from this software.