1) Go to CCSM->General Options->Commands tab
2) Under "Commands", you can define up to 12 entries.
|Run dialog:||dcop kdesktop KDesktopIface popupExecuteCommand|
Global shortcut conflicts (Amarok example, most KDE programs work analogously):
Amarok shortcuts seem to be generally window-manager-independent, however, conflicts are resolved in favour of compiz. This usually affects Win (Super) + C (Enhanced Zoom/Group and Tab Windows) and Win + Z (Put Windows).
The easiest way is to change your Amarok shortcuts: Amarok->Settings->Configure Global Shortcuts…
If you want to keep the Amarok shortcuts and to know exactly which compiz plugin is blocking your shortcut, do a grep (found here) in /etc/gconf/schemas:
grep -A 2 '<Super>c' /etc/gconf/schemas/*.schemas
(XML file, so use HTML string notation. Example for <Super>C, adapt if necessary). Either change the shortcut directly in the affected .schemas file (check whether the plugin is active), or use the CCSM GUI.
Global shortcuts are managed in the Personal Settings manager (Keyboard & Mouse) for all KDE4 applications.