I've used this keyboard on 10.5.8 on two different PowerMac G5s, worked perfectly. There is a software update for it that properly maps the keys. It might download automatically in "Software Update," or you may need to download it from Apple, but it works, and all keys function correctly.
For those that don't want to have to look up the model number, the OP is talking about the full aluminum wired Apple keyboard with number pad. (would have been easier to say that!!)