Ps/2 KVM used to be good
but now in days it is becoming harder and harder to use those
a USB KVM is definitely the way to go
the Linksys one i mentioned has Both USB and PS2
so you are safe on that area, nothing to worry about you've got 100% support for old and new hardwares.
the only thing missing from that great KVM is Sound and MIC
but heck you can't get anything perfect these days, and the Linksys USB+PS2 KVM is the best that you can find.
Now if i can only get the 8 port version of it then it'll be great
even the 4 port version was hard to find
i was forced to use several 2 ports on 2 ports on 2 ports on 2 ports to control all my rigs (cascade flow 6 > 3 > 2 > 1)
it's kinda cool in a way, it allowed me to be more flexible and be dualing keyb / mouse 2+ rig at the same time, rather than limited to just 1 keyb/mouse as it would have been if i was using a 4port or 8port
the only trouble was to memorize at any given time and moment which switch i'm on