Mark,

What is probably required here is some ferrite chokes.  Please try the
following:

    1.  Purchase or borrow some ferrite torriods.
    2.  Wind at least one full turn of your PS2 cables onto the ferrite
torriods. (One cable per torriod.)
    3.  Retest the equipment.

If this allow the equipment to pass, then you must include the ferrites within
your computer if as per your original post the keyboard and mouse cannot be
altered.   I have seen this done on several computers.  It is fairly easy to
mount the PS2 connectors on an expansion "blank"  similar to how many serial
ports are connected.

Another possible avenue to explore, is to replace the PS2 connectors on your
motherboard with shielded types.   AMP and other connector manufacturers make
special low EMI connectors.

Please note that many of the better keyboards and mice today have ferrites
molded into the end of the PS2 plug.  Perhaps you just need to find a keyboard
and mouse that will pass with your present computer.

Good luck.

------ Steve

PS.  Radio Shack and other electronic houses sell clamshell type clamp on
ferrites that are also useful for testing.