Here is the beta AppleACPIPS2Nub I have revised. It will work with any version of AppleACPIPlatform without editing the info.plist. Hopefully, in the future, we don't have to worry about AppleACPIPlatform being updated and losing the PS/2 devices.
It is based on original dfe's ACPIPS2Nub. (http://www.tgwbd.org/darwin/extensions.html) I have tested it with 1.1.0 and 1.2.1 of AppleACPIPlatform and it works. Make sure that you don't have ACPIPS2Nub Installed or it will cause error.
Again, it is just the beta version and backup the original ACPIPS2Nub before trying it.
1. Cleaned up.
Update: 7/23/2008, 8/2/2008
1. AppleACPIPS2Nub_b5: Fixed PS/2 keyboard working without PS/2 mouse existed in the system.
2. AppleACPIPS2Nub_Mouse: Fixed PS/2 mouse working without PS/2 keyboard existed in the system.
AppleACPIPS2Nub_Mouse is basically the same as AppleACPIPS2Nub_b5. In the AppleACPIPS2Nub_b5, mouse is attached to keyboard while in the AppleACPIPS2Nub_Mouse, keyboard is attached to mouse.
(You might need the modified ApplePS2Controller to make your PS/2 devices work if your system ONLY has PS/2 keyboard OR PS/2 mouse existed.)