Q: Help With Wireless Keyboard Please

I have a 10.5.8 OSX and recently purchased the Wireless Keyboard to replace my old one when some of the keys stopped working. None of the function keys are working properly. F9 and F10 darken out the desktop, F11 slide whatever I'm working on out of the way to go to the desktop and F12 goes to the dashboard. I have tried downloading an update from Apple Support that was supposed to fix the problem after I deleted the keyboard and readded it and it didn't work. I have searched the internet for solutions and it seems alot of people are having this problem. I'm assuming that my operating system is "too dated" and that I need a 10.6 and later for this to work right but that is not what was indicated on the box at the time of purchase. Please help if you can. Thanks!