PS/2 to USB Converter - Excerpts from Customer Support
I bought the PS/2-USB adaptor just to use with a PS/2 mouse and keyboard with my iMac (running MacOS 8.6). The mouse is a Logitech 4-button contour mouse with a wheel.
It basically works OK except that the mousewheel doesn't work and the Logitech control panel/extension is disabled (i.e., it doesn't detect the mouse at boot time).
Is this a likely side-effect of having the adaptor in place and the possibility that the software doesn't recognize the mouse as an appropriate device for a USB-based iMac? Note that this mouse is a PS/2-USB combo device ("native" USB with a PS/2 adaptor plug).
[I should also mention that I am running this rig through a KVM switch that has 3 PCs on it in addition to the iMacm, hence the reason for buying the adaptor in the first place. The signals are getting through well enough so that the keyboard and mouse basically work, so I don't think the KVM switch is really a problem. The mousewheel works OK on the PCs, but they are, after all, expecting to see a PS/2 mouse.]
I found a work-around. I disabled the Logitech Mouseware control panel/ extension and re-enabled USB Overdrive (shareware USB mouse/joystick mgr) and was able to get basic 3-button wheelmouse functionality to work with at least some apps by programming the mouse via the control panel (right button => control-click, wheel => scroll up/down, etc.).
P.S. When setting up USB Overdrive, it looks like you have to set the wheel operations to be "backwards" (e.g., Wheel Up => Scroll Down) to get the desired action for a given input.