Ok... since this is the only source for this information that I could find on the web... I'll add to this very old post!
I have a X-Arcade dual (2 player) and I recently wanted to hook it up again but misplaced the PS/2 keyboard part of the adapter (female serial to male PS/2). So it seemed logical to try to build this with an old keyboard for the PS/2 end and a serial cable. Problem 1: the keyboard did not have all the wires in the cable to the PS/2 end. Lesson learned and I just cut off the end to solder the wires from the serial cable directly to the end.
So all I needed to know was which wires go to what pin. With the magic of searching, I found this thread. I tried both the diagrams above (they aren't the same) and neither worked. The red light comes on the X-Arcade, but I get a keyboard error on boot and no lights on the keyboard.
So this led me to try one last desperate act... I searched harder and found the original adapter.
Curiosity got the better of me and I decided to trace the wires. Here are my results from the actual X-Arcade Serial to PS/2 Adapter cable: