Having played around with a similar problem, perhaps I can help with this:
Firstly, my setup:
-Box1 is a notebook running winXP
-Box2 is a VIA motherboard running Mandrake 9.2
-Keyboard and mouse are a Logitech Cordless Desktop (The older version, without all the multimedia buttons.)
-Switch-box is a cheap mechanical one; two pc's, each channel with two ps/2 and one vga connection.
The problem I experienced:
-When booting up, I always make sure that the pc currently booting has the keyboard and mouse.
-Works fine in Windows, I switch to Linux, works fine.
-But then, as soon as I switch back to Linux, no more keyboard. (I dont know about the mouse as I use different mice for each pc.)
-When I unplug the keyboard cable going into the windows box and plug it back in again, it works fine again.
I took the mechanical switchbox apart and found that the 5volt supply pin of both computers is connected to the keyboard input at all times, regardless of the switch position, by means of two diodes. So, whichever pc outputs a higher supply voltage supplies power to the keyboards.
I suspect the logitech wireless receiver does not like being switched around between two clock signals without being reset (ie re-powered up).
The fix I am planning is the following: If I place a little push button next to the switching unit's switch I could "reset" the keyboard by pushing this button and thereby disconnecting the power to the logitech wireless receiver for a second or so.
ie. every time the mouse/kboard/monitor is switched I would afterwards press this button and "simulate" the keyboard being plugged out and back in again....
Will let you know if it works (Once I find the time to actually try it out
, meanwhile its back to plugging everything around manually...)