How can I remap the volume buttons for custom use? First of all, I only want to disable the standard volume buttons - I do not want to disable the buttons to change brightness, launchpad... 

I need this because I want those buttons to trigger scripts for finer volume adjustment using FastScripts.
Karabiner (Formerly called KeyRemap4MacBook)

allows to intercept the keyplay.


Assign your scripts for fine volume adjustment to F11 and F12 (actually it's a combination of fn+vol. up/vol. down).
Download and install Karabiner.
Open the Karabiner preferences via the menu icon, which is a black square (like a keyboard key), somewhere in your menu bar.
In the Tab Change Key select the options:


Volume Down to F11
Volume Up to F12
F11 to Volume Down
F12 to Volume Up


This will switch the behavior of the function keys with the volume keys: Now you can use fine volume adjustment with one touch and the usual volume adjustment using fn+vol. up/vol. down.

Note that there is also an option "Fine grained volume controls" that enables fine grained volume controls by default, so you can do this purely within Karabiner, without any other scripts.  You can find this in the giant list, under "Change F1..F19 Key &amp; Functional Key" and then the submenu "Change Functional Key".