RE in Leopard you could add/change keyboard shortcuts via the homonymous tab on the Keyboard & Mouse Preference (System Preferences, Hardware):
There ain't no such thing in Lion; Keyboard is way pared down.
On my old iMac I could assign virtually anything to the function keys, especially certain frequently used applications such as Word or my browser access [....]
You can create keyboard shortcuts only for existing menu commands. You can’t define keyboard shortcuts for general purpose tasks such as opening an application or switching between applications. (Emphasis added)
