My father has a Compaq 700Mhz slim PC running Windows XP. This has the two standard PS/2 ports, with a (French) keyboard and a mouse attached to them. For his studying he needs a Russian keyboard which I have finally been able to find (HP model I would say circa 2002 from the design), but this hooks up to PS/2.
The PC is a bit limited in USB and expansion slots (all already fitted), and his original keyboard is fine. I know of various ways of connecting this additional keyboard:
Add a PCI board with a PS/2 keyboard port on it, but won't there be an IRQ conflict or whatever as the onboard PS/2 keyboard port works and I don't intend to disable it. Would the revision of PCI have any importance in this case? I have seen combo cards with usb and PS/2 ports (as listed at it.us.syba.com), but those are PCI2.2 and I'm not sure the computer is even PCI2.0!
Add a PS/2 (kb and possibly ms) to USB adapter. I read at some places that they don't need any driver but how is this possible (I don't know if any of the PS/2 keyboards I have supports such direct plugging or detects when it's plugged to USB)?
Add a USB docking station with PS/2 ports, which is possibly just the same as option 2 plugged on a USB hub (or does it have some additional circuitry to cope with the PS/2 ports? and the corresponding driver?)
I know this will not allow two sessions on Windows, and the keyboards will be used alternatively (and the language setting need to be changed accordingly). As my father is far from touch-typing, it's better to have the actual keyboard, especially when the alphabet is different.
Can anyone advise me and possibly explain how the various options work so that I make an educated choice? Maybe I would have no risk of conflict if my onboard PS/2 keyboard port was dead, but this is not the case. As a sidenote, I would not be in such a trouble if I wanted to use two mice as they do not depend on the language in which you type and I would have one more option than USB before reverting to a second PS/2: the serial port.

