There are generally four different kinds of mice:
- Bus mouse
As often motherboards predating Socket 7 lack USB (and older ones may even lack PS/2), a serial mouse is almost a must for playing older Windows games, but these are hard to come by these days (particularly mice that have a scroll wheel).
Adapters to make a PS/2 mouse fit in a serial connector exist, but the mouse itself must be able to support the serial protocol or it won't even work. The pinout of these adapters is not standardised, so adapters from one manufacturer may notwork with mice from another company.
PS/2 expansion cards are virtually non-existent, and USB expansion cards have the drawback to requiring a relatively large amount of CPU power (so it's not always a good idea to use such a card in a 486). On top of that, many USB cards won't fit a 486's PCI slots as said PCI slots often are incompatible with newer USB expansion cards.