Do I want a PS2 mouse or do I want a USB/PS2 mouse ??
That does not matter. Just make sure that it is supposed to work with PS/2. Such USB/PS2 mice come packaged with an USB to PS/2 adapter. Mice which come without such an adapter are USB-only and don't work with an adapter from another mouse. If you cannot examine the package, read the manufacturer's description. If it says the mouse works with both USB and PS/2, it will. If the description does not mention PS/2, it probably won't work.
I am using a Logitech Cordless Optical mouse with a 4-way KVM switch and Cocolino PS/2 to Amiga converter. The only problem with the KVM switch is that wheel movements are not transmitted correctly, so the wheel cannot be used.
Bye,
Thomas
