Function keys, or F-keys, are special-purpose keys on a keyboard that allow you to perform certain actions on your computer quickly. These keys comprise the top row of keyboards and are labeled F1 ...
You could reassign the keys needed for Exposé and Spaces, no? I have a early 2008 MacBook so all F-keys except F5 and F6 are occupied by various system control buttons (play/pause, dashboard etc).