bobw said:
I guess I should have clarified. You CAN use a two-mouse button on Mac OS 9 and below, HOWEVER all the buttons would act as a "normal click", if you will, instead of having separate actions. This can be remedied as mentioned by Mikuro by the software PROVIDED BY THE MANUFACTURER OF THE MOUSE, or some third party software. It doesn't work right-out-the-bat in Mac OS 9 and below as it would with Mac OS X.
On my Motorola StarMax Macintosh clone, for example (jsut to complicate things a little further

), I have two PS/2 ports. I have a regular PC mouse connected to the PS/2 mouse port, but both buttons act as a "left click." I had to download a piece of software written by another StarMax owner called Mouse2B which could map the right-click to anything I wanted. This was the only way I could do it on this particular machine with this mouse on this port.
Had I bought an ADB (pre-USB device ports on older Macs, which my StarMax also has) mouse with more than one button, I'm sure it would be the same...both would act as a left click until I installed the accompanying software.