While this thread seems to have resolved itself, there are two things to note. Adessa has made, and still does make Mac compatible keyboards. If the keyboard they offer is USB, it should work on a Mac. The extra keys and "functions" may not.
A KVM switch will that accepts PS2 plug keyboards and mates to a USB input on the computer may also solve the keyboard incompatiblity. I did just that when I set up my old G5 tower for my wife's use. She uses a Thinkpad with an old external Dell Quietkey PS2 plug keyboard. The switch functions flawlessly.
