When you are sitting at a Mac computer, the function keys (F1, F2, etc), perform special actions, like volume control or window management. By default, if you are in a Remote Control session and press a function key, the appropriate command will not be sent to the host computer, but instead will start the corresponding action on the Mac.
It is possible to disable this default behavior. To do so, while sitting at the Mac, go to System Preferences > Keyboard and Mouse. Under the Keyboard Shortcuts tab, you must uncheck every box next to an action that is associated with a function key. On Mac OS 10.5 Leopard, you should also check the box under the Keyboard tab that says, "Use all function keys as standard keys."
Keep in mind, doing this will disable the special Mac shortcuts.