I'm having the same problem, running OSX 10.5.8 on a MacBook. Bought the wireless keyboard last month, have read through the discussions here, and none of the solutions work. Use all is unchecked, and the volume/screen brightness keys still don't work. Unchecking the keyboard preferences for F10, F11, F12 will prevent the keys from showing the dock/apps, but the keys still don't adjust the volume - they just become dead keys.
Any further suggestions? It's a minor thing, but it does impact the ease of use and for the money spent on this keyboard, I'd expect the minor things to work.