I'd be doubtful that the distro(s) would ignore the ps/2's yet, so
It may be that your mobo is set in 'advenced configuration', or somewhere like that, to 'usb legacy devices' or such (meaning: claim kbd & mouse), thus either the BIOS has disabled the 'classic' ports, or the distro(s) are checking there first, and the BIOS, usb-kbd attached or no, is claiming to have one, thus the distro(s) are only looking to usb for a keyboard.
I have a Kensington trackball on ps/2 and a K. wireless/optical/scroll-mouse on USB. 'Ball is my usual, but I use both, so my Shuttle mobo has 'legacy' ON, but usb only claims what is really attached. Thus for me,most things find the ps/2, some find both (
), but a few things find only the usb mouse.
I repeat, with my ps/2 & usb rodents, some find one, some the other, and some both, so I suggest:
Try checking through the BIOS for anything like 'legacy' or 'classic' or 'ps/2' or 'mouse' or 'kbd'/'keyboard' as USB, and try disabling it as a test... Continue from there as you see fit if it works.
P.S., you said '64', and of course we both know that newer mobos (& 'stuff') are all heading to usb & leaving the classics behind, and I suppose I conceed that this is for good reason, but the '64' *probably has usb-legacy=ON as original default, and *might* not even have a "switch", so your choice of distro may be constrained by this.
***AND***, I have seen linux accept one rodent, and an app under it insist on using the other, so watch out for this too, if, once all is running, you find an app not responding -- it may be looking for the other rat, present or not!, so maybe you should have one of each handy... !?!
**Now**, if this app-wants-other issue arises with kbd, ... Well....