so 2 PC's but one set of keyboard, mouse and monitor?
when my KVM switch died, the newer models had left me behind, it was impossible to get PS/2 and VGA KVM boxes.
so there's your first hurdle, what monitor ports to you require?
and are any one of those 3 peripherals likely to change?, forcing you you potentially change KVM's again.
in the end it was simply easier and cheaper to get another keyboard, monitor and mouse.
also, when flicking the KVM between rigs, does yours ever not pickup the change-over?
something like 20% of my flick overs just wouldn't get accepted by the other system and I had to reboot that rig anyway to pickup the k/b and mouse.
overall, not a satisfying experience with KVM's.