This project makes up a small PCB that you can use to connect an older AT style motherboard with a newer (easier to find) PS/2 keyboard.
Solder some pins taken from a pin header to the bottom of the board that correspond with your motherboards original AT connector after you remove it.
Next solder on a standard PS/2 socket to the other space on the PCB.
The surface mount footprint is for a 100nF capacitor if you feel the need.
Though untested, the opposite of installing an AT connector for a PS2 keyboard with this adapter should also be possible where room exists on the motherboard.
NB: cut the pins going up from the AT motherboard to the adapter board flush at the top and ENSURE THAT NOTHING SHORTS OUT on the shielding of the PS2 connector. Also cut the pins for the PS2 connector flush at the bottom to give good clearance.