Right now though I'm running MSN Messenger 2.5 on Mac OS 9.1, thanks to GestLab, a program that lets you change Gestalt information about your computer (such as which version of Mac OS you're running). The developer's website can be found at
http://gestlab.free.fr/gestlab/glab_us.html. Once GestLab is downloaded, you just need to change the "sysv" selector to "00000922" Then, you can install and run MSN Messenger 2.5 on Mac OS 9.1!