New iMac keyboard help

I just got one of the new iMacs, and it is my first Mac, and I read somewhere that on Mac keyboards the three shortcut keys for expose are f9, f10, and f11. but on the new keyboards, those keys are used for mute and change volume. is there a way that i can make it so those f keys will work with expose?

F3 is expose, F4 is the dashboard.

then do you know the keys to automaticly hide every window to show your desktop?