Perhaps you have already solved this. But for other imac bluetooth keyboard u sers:
Keyboards for MAC OS X have a very economical programming for use of keys.
1. Keys do not produce the letters on your screen, or at least one does not. GO to System preferences, Speech, click on Key to enable speech, and if it is a normal character, change it to a combination like option plus + sign. Using a normal character alone to to this enjabling, nullifies its use as a character!
2. All your function keys do not respond! If you have tghe new bluetooth keybord, this has a dual function. Top row can be the ordinary function keys. And if you want the functions indicated by the ikons, just press fn plus the ikon you want. OR in Systems preferences, Keyboard, unclick 'enable all function keys to work normally' and these will revert to the functions indicated by their ikons. Then to use the function int he ordinary way, press fn and the desired function key. All of above is clearly explained in mac user:
http://support.apple.com/kb/HT3399
Impala