How to remap "Dashboard" key to show the Desktop on OSX [Snow] Leopard?

It's certainly no solution - but just to add to the conversation: by default hitting command+(Show All Windows) shows the desktop. i.e. hitting command-F3 where F3 is functioning as a special key and not truly as "F3" If nothing else, it's an easy reach on the keyboard and somewhat logical. I still can't understand why there is no show desktop special key - especially in light of the dedicated dashboard key (who uses that?) and an empty space at F5.

Try KeyRemap4MacBook:

KeyRemap4MacBook is a powerful utility for keyboard customization.

The re-mapping of the key more than 500 kinds.
Accelerate speed of the key repeat.
The revival of a lost NumPad key (FN+jkluio789…)

After you install it open the preference pane, expand "Change functional key (brightness, volume...)", and scroll down a bit for checkboxes that let you remap all the built-in keys to F-keys.